The question was not about Rabbi Moshe Landau, because as stated it is hard to find explicit statements from him on the subject, but about his son Chaim Yitzchak Isaac Halevi, who for some time has been accompanying him as his successor in kashrut matters, and apparently that is how it will continue. The yeshiva where he teaches (according to reports on news sites) is packed with messianic symbols as I mentioned (they have a site at http://chabadzefat.com, and it is not hard to see their messianic belief there).
As I understand it, the credibility of kashrut bodies comes by virtue of the rule that a single witness is trusted in matters of prohibition, and therefore the question is whether a person who does not believe in the coming of the Messiah (who according to many opinions is judged a heretic) is trusted for something that requires one witness. I would add that even if we do not suspect him of believing in the Rebbe’s divinity, the judgment and common sense of a person who believes in the Rebbe’s messiahship are highly questionable.

There is a story about the Chazon Ish, who once spoke at someone’s funeral against a certain thing he had done improperly (I do not remember the details), and they asked him: is this the time to bring that up? The Chazon Ish answered: if I had not thought it necessary to come out against him on this matter, I would never have said it. But since that person made a grave mistake in that matter, I am obligated to protest
and to say these things.

Correction: the son’s name is Chaim Yitzchak Isaac Landau.

I explained that if he is trustworthy regarding kashrut, there is no obstacle to accepting his testimony. A single witness is trusted in matters of prohibition even if the witness is disqualified from formal testimony, so long as his testimony is factually reliable. That is why a woman is trusted, and a relative is trusted, etc. In a place where one witness suffices (in matters of prohibition and not for an oath), the point is that there are no formal restrictions on credibility, and a factually reliable clarification is enough.

I do not think that is accurate. An apostate who sins out of spite is disqualified even for testimony regarding prohibitions; see Yoreh De’ah section 2. It is implied there that he is disqualified both from slaughtering and from testifying about the slaughter, and the same applies to an informer as explained there.
And it stands to reason that the same applies to a heretic, because everywhere Maimonides includes sectarians, heretics, and apostates as one unit (and according to Maimonides, one who denies the coming of the Messiah is included among heretics).

An apostate is not disqualified in matters of prohibition except where there is concern that he is lying. As stated, there are no formal disqualifications of testimony in matters of prohibition.

That is not what the Shulchan Arukh says there. An apostate who sins out of spite is disqualified because he is worse than a gentile (and even with a gentile it is not clear whether he is fit for testimony in matters of prohibition), and not because of concern for lying. An apostate who sins out of appetite is disqualified because of concern for lying.

In any case, now I see that at the funeral this Chaim Yitzchak Isaac was also appointed rabbi of Bnei Brak (besides Landau’s private kashrut certification), and he will also deal with the religious affairs of Bnei Brak together with another Lithuanian rabbi. And this is really a disgrace and a shame, to appoint a person who is an openly declared messianist, who according to many approaches is judged a heretic, and whose views certainly border on insanity, as an official rabbi supposedly in the name of the leading rabbis of the generation. Simply shameful.

Even a gentile is fit for testimony in matters of prohibition on the assumption that he is reliable. This is an old topic, and the medieval authorities and later authorities discussed it at length. Testimony in matters of prohibition is nothing but an evidentiary estimate. You need to clarify reality, and there are no formal rules here at all. When someone writes that so-and-so is disqualified from testimony in matters of prohibition, it is simply because he assumes that person is not trustworthy in that regard.

It is no small audacity for someone who published the following on Behadrei Haredim on 9.6.17 [and from the style there, the writer speaks about himself in the first person and it sounds like he is Michael Abraham himself] to claim that he has problems with what someone does in his beliefs. And these are his words [the following are quotations from an article reflecting his opinion as published there]:
1. The Talmud is not free of errors
2. It also contains quite a few halakhic mistakes
3. There are quite a few recommendations of the Talmud that are not correct for our times
4. Hebrew Bible and Prophets… to the best of my estimation, even a prophet can make a mistake
5. The description in Genesis stands in rather frontal contradiction to the theory of evolution
6. There is room not to accept some of the laws of prayer that are based on mistakes [regarding God’s involvement in the world; that is what he wrote there earlier]
7. The medieval authorities, with all due respect… they too could make mistakes
8. The same applies regarding questions of providence and God’s involvement in the world, and certainly regarding the Messiah

Someone who opens his mouth with contempt against everything holy and precious to Israel, including saying that prophets can make mistakes, including the belief in the coming of the Messiah—he is the one talking about heresy?????????????????
Yuckkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkk

🙂

This is irrelevant. There is a halakhic question here whether one may rely, for kashrut purposes, on a person who denies the coming of the Messiah and who according to many views is defined as a heretic. And the answer should be substantive.

In any case, I find it hard to accept the answer that an apostate and a wicked person are trusted in matters of prohibition, because in Shulchan Arukh Yoreh De’ah section 2 it is explained that an apostate who sins out of spite is disqualified from testimony about slaughter, and I have not been given a source that contradicts this.
Second, even if we accept that an apostate/heretic is in principle fit for testimony regarding prohibitions, what advantage does Landau’s kashrut have over any very basic certification? And who guarantees us that Landau’s kashrut standards are the most stringent? In the end, nobody is capable of checking this, certainly not regularly, and all we are left with is the word of the kashrut supervisors. And if the fish stinks from the head, it is very hard to rely on them.
Third, a person who believes that the Rebbe is alive and is the Messiah is cuckoo and crazy, and I would not rely on him in much simpler matters.

(This reminds me that at the Mayanei Hayeshua hospital one of the senior doctors there is Professor Eliyahu Sorokin [he treated many rabbis such as Rabbi Steinman and others], who is a Chabad messianist with a “Long live our master…” kippah on his head. In the past he was also a bit Christian according to Wikipedia, so everything fits.
And it is truly bizarre that people rely on such a creature in matters concerning their lives. After all, medicine is not an exact science; for the most part it is based on assumptions and evaluations, so how can one rely on the judgment of such a kook on the most important and precious matter for every person? More than that: the main role of a doctor is to save people’s lives, which means that at the very least he is required to distinguish between the living and the dead, whereas this person cannot even do that, because he claims that a person who died about 25 years ago is still alive [and no less than the Messiah]. So how exactly can one rely on such a creature in such a serious and important matter?? It is beyond me.

Yudi,
These are childish arguments. There are quite a few intelligent people in various fields who believe nonsense. Do you know how many crazy people populate mathematics and physics departments in universities? Very smart people whom one can rely on in every matter, but they have bizarre beliefs and bizarre practices. By the way, Jewish law also recognizes this phenomenon. It is called being insane with respect to one matter (and perhaps this depends on the dispute at the beginning of tractate Chagigah whether we require all three signs or one is enough, though that can be rejected).
The world is complex, and in recent generations we have learned to understand that. Anyone who knows the world knows there is not necessarily any connection, and if a person is insane in one matter, one can rely on him in other areas. His kashrut prestige is well known, and therefore his beliefs are irrelevant here.

Notice that many people would also say about you (and me), as someone who believes in God, that you too are insane in one matter (you believe in imaginary friends) and cannot be relied upon. A person’s beliefs are the result of many things, among them dogmas, meaning things one is obligated to believe. That is not necessarily the result of his own independent judgment.
By the way, according to you, is someone who believes that our forefather Jacob did not die, or believes in Elijah the prophet, fit for testimony and to grant kashrut certification? So what is the difference? That he is alive in our time and they were long ago? And what about all the Hasidim who believe the stories about the Baal Shem Tov? And what about those who believe in the resurrection of Talmudic sages?
I get the impression that you have something in your heart against Chabad, and therefore you are drawing hasty conclusions that do not arise from reality, just in order to exclude them from the fold. Get over it. I do not like them either, but the conclusions need to be measured—especially in a discussion where you are making claims about the quality of someone else’s reasoning.

As for the disqualification of an apostate who sins out of spite, I already explained that no contradicting source is needed. He is indeed disqualified, but that is because in the time and place of the Shulchan Arukh he was presumed not to be trustworthy to tell the truth in these areas (but not because of an intrinsic personal disqualification). Therefore, in a place and time where he is trustworthy, he is fit for testimony. Even secular courts are trusted where they would not undermine their own credibility, but a Jew who is hysterically strict about kashrut, and even if he were an idol worshipper, would not be trusted? In the same way, some halakhic decisors validated the testimony of Sabbath desecrators in our time (even for actual testimony, not only for matters of prohibition) because they are careful to tell the truth.

In 2003, a responsum by Rabbi Aharon Feldman, head of Yeshivat Ner Israel in Baltimore, was published, in which he wrote that those among Chabad Hasidim who believe their rabbi will rise from the dead as the Messiah—their belief is false, but they are not heretics. In contrast, those who believe that “the essence of divinity” was clothed in Rabbi Menachem Mendel Schneerson and pray to him are heretics and may not be counted for a prayer quorum.
Source:
https://he.m.wikipedia.org/wiki/%D7%90%D7%94%D7%A8%D7%9F_%D7%A4%D7%9C%D7%93%D7%9E%D7%9F#cite_ref-2

And see here:
http://web.stevens.edu/golem/llevine/feldman_berger_sm_2.jpg

And here:

יש ללחוץ כדי לגשת אל feldman.pdf

In any case, the problem is who the supervisor is and who the slaughterer is, and that problem remains even when a Lithuanian rabbi is also appointed…

Indeed, that is a problem, because even if we accept that an apostate is fit to testify about kashrut, in any case he is disqualified from slaughtering. (I do not know who controls Landau’s kashrut, but I suspect that with the appointment of Yitzchak Isaac Landau, he will make sure to place as many messianists and the like there as possible; that is usually their pattern of action.)

It is not so clear why they are not considered heretics, since not a single one of the Messiah’s signs was fulfilled in the Rebbe. Even regarding Hillel, who said in tractate Sanhedrin that Israel has no Messiah because they already “consumed him” in the days of Hezekiah, the Book of Principles wonders why he is not considered a heretic, and answers that this was an error based on what he believed and understood, which is not considered heresy. But with Chabad this is just a heap of explanations that do not stand up to the scrutiny of any halakhic decisor. (And as stated, Maimonides rules that one who denies the coming of the Messiah is considered a heretic.)

By the way, be sure that if Rabbi Landau’s son had taught for even one minute in a Religious Zionist yeshiva, he would already be burnt goods among the Haredim. But when he taught for decades in a messianist yeshiva… that is not so terrible, since over there they have jackets and hats, and white shirts… according to the pure and pristine worldview…

According to this, Sabbateans, Frankists, and believers in Jesus are in principle trustworthy to testify about kashrut.

What about participating in a Sabbath meal or Passover Seder organized by Chabadniks when you do not know how deeply, inwardly, they are messianists/divinizers/believers in incarnation?

Indeed, they are trustworthy. Is this meant as a reductio ad absurdum? In my view it is a reductio ad trivialum.
I did not understand your question about participating in the meal.

1. I just heard from a friend that even among the Lithuanians there are concerns about this same Chaim Yitzchak Isaac Landau. According to him, there was something very strange about the crowning of Rabbi Landau’s son at his father’s funeral alongside Rabbi Shevach Rosenblatt. In reality it is impossible to appoint both of them as rabbis of the city of Bnei Brak, because one slot is designated for a Sephardi rabbi (according to the law, and indeed until recently the rabbis of Bnei Brak were Rabbi Korach and Rabbi Landau, who has just passed away). So what is the meaning of this joint crowning (which is still not official)? The answer is that the Lithuanians are indeed very afraid to place all the religious affairs of Bnei Brak in the hands of that messianist (already today there are no shortage of Lithuanians who do not trust Rabbi Landau the father’s kashrut certification because of Rabbi Shach’s battles against him). And they are doing everything they can not to abandon this arena.
And by the way, this fits Rabbi Feldman’s words quoted above: even if there is no principled problem relying on them, certainly it is not recommended ab initio, because it is very hard to rely on their judgment.

2. There was no response to the distinction raised above between the possibility of relying on the testimony of an apostate and validating his slaughter, since the slaughter of a gentile or a heretic is certainly invalid. (And likewise their Torah scrolls, tefillin, and mezuzot.)

3. I emphasize that I have nothing personal against Chabad. My main problem is with their primitive herd-like faith (which, by the way, I really do not agree they clearly distinguish between the Rebbe’s messiahship and his divinity; for them it is all well mixed together), and the big problem is their evasive answers and whitewashing attempts whenever it comes to a principled discussion. They twist themselves into sophisticated answers regarding their belief. (This point too was raised in Rabbi Feldman’s letter above, and also in the book of David Berger to whom the letter was addressed.)
Try sometime to extract from a person known not to be a messianist a clear statement in the style of “the Rebbe is not the Messiah,” or to extract from a messianist a decisive statement that… in my experience you will not succeed. And note that if these were serious people, you would long ago have seen total repudiation by the non-messianists of the messianists, and total repudiation by the messianists of the divinizers.

4. The claim raised above that we too have superstitious beliefs is not correct. After all, you are the one who argues and explains how rational belief in God and the Torah is, whereas identifying the Rebbe as Messiah or God does not meet any test whatsoever. They do not claim to have new signs of the Messiah; rather they explain in a crooked and twisted way how all the signs of the Messiah were fulfilled in the Rebbe. And indeed I think that if you identify in someone a pattern of baseless and irrational belief, it is very hard to rely on his general judgment, unless we assume he has some personal stake in believing that belief and therefore holds it. But then there would be a problem relying on a person who, for personal interest, is willing to accept bizarre beliefs.

Small correction (end of section 3):
Try to pressure a messianist into saying that the Rebbe is not God—there is no chance you will succeed…

Some people would understand it that way. But mainly I wanted to make sure, because it is surprising, though of course surprise is not a halakhic criterion.
The question about participating in a Chabad Seder night is that it is a thanksgiving meal, and the boundaries between ordinary Chabadniks, messianist Chabadniks, and divinizing Chabadniks are unclear. So the situation is that it is unclear to which god exactly thanks are being given: to the Creator of the world, to the one who was incarnated in the Rebbe’s soul, or to the Creator of the world in partnership with the one incarnated in the Rebbe’s soul?

For anyone interested: first of all, Rabbi Shach already came out against Rabbi Landau the father because he was identified with messianic Chabad, and therefore he was never officially appointed rabbi of the city of Bnei Brak (source: Wikipedia on Rabbi Shach). Second, the Lithuanians apparently do not really trust Rabbi Landau the son either, and therefore attached Rabbi Shevach Rosenblatt to him.

The rabbis of HaPeles, on the other hand, strongly oppose appointing Rabbi Landau’s son to the rabbinate of Bnei Brak.
https://mobile.kikar.co.il/article/313217

The belief in the Rebbe as Messiah and the proclamation “Long live our master, teacher, and rabbi, King Messiah, forever and ever” appears in a halakhic ruling by rabbis from all circles; attached is a link:
chabadpedia.co.il/index.php/ruled_the ruling_that the Rebbe_he_king_the Messiah

The great Rabbi Aharon Soloveichik of blessed memory published a “declaration of opinion” on 7 Tammuz 5756 in all the Jewish newspapers in the U.S. (translated from English):

The following is my response to the many questions about my position regarding Lubavitch and their messianic belief.

Before 3 Tammuz, I counted myself among those who believed that the Rebbe was worthy of being the Messiah. I believe absolutely that had we—especially the Orthodox community—been united, we would have merited the complete redemption.

Regarding the belief of many among Lubavitch (including prominent rabbis and heads of yeshivot)—a belief based in part on similar statements by the Rebbe himself about his predecessor, the previous Rebbe—that the Rebbe can still be the Messiah, and this in light of the Talmud in tractate Sanhedrin, the Zohar, Abarbanel, the writings of the Arizal, Sdei Chemed, and other sources, it is impossible to dismiss it as a belief outside the Orthodox stream.

Out of a letter by the great rabbi, head of the religious court of Montreal, Rabbi Pinchas Hirschsprung of blessed memory, published on 13 Iyar 5757:
I hereby state my clear opinion on this matter (without expanding on all the give-and-take, since I have already heard the matter in all its details, and this is not the place to elaborate):

All the discussion and debate regarding the singing, the printing, and the matter of “Long live the Rebbe, King Messiah, forever and ever,” and everything involved in it—there is not even a trace of a halakhic question here, and it has sources in the Talmud explicitly, in the Zohar, and in the great kabbalists upon whom we, all the Jewish people, rely also in practical Jewish law. (Aside from this, the Rebbe of Lubavitch was a great rabbinic authority etc.—in the category of a master comparable to a tanna—and if he used these words regarding his father-in-law of blessed memory, and hundreds of times, that itself can already be a source and an authoritative basis.)

And similarly regarding ways of influencing our fellow Jews, etc.—the Rebbe of Lubavitch, and the Chabad Hasidim themselves, have already proven both the man and the amulet, and who knows better than they what the proper approach is to bring fellow Jews near, and in a way that only this and not another, etc….

And Rabbi Hirschsprung adds in that same letter and says:

Whose opinion will be accepted more—the opinion of Lubavitch, who work in all corners of the globe and the U.S. in particular, with great friendliness, and are continually winning the hearts of fellow Jews, or the words of some rosh yeshiva (or even several of them)? For when Lubavitch prints the basis for their practices, showing how it is founded on the words of the sages in both the revealed and hidden dimensions of Torah (and on the Rebbe’s own words), what will it help if one person says it is merely his own “Torah opinion”?

Bless us, our Father, only when we are all as one. And may God bless His people with peace.

Indeed, foolishness is not necessarily idolatry.