Happy Monday of postcards

Thank you.

A. Same as for Rosh Hashanah, two days?
B. To what extent is this halakhic in practice (not from the perspective of the halakhic perception of Judaism today)? That is: would we say this is at the level of a small thing that can be canceled personally? (Clearly these are two completely different things and the reason for the permit is also different)

A. There is no difference.
B. No. This is a rule that was established in the Great Court and a person cannot revoke it even if his reason is invalid. Legumes are not a rule but a concern that was practiced at some time and was not determined by an authorized court. See the article on Legumes

It is not clear that this is a rule established in the Great Law; simply put, it is a normal rule of doubt from the Torah to the grave, which was used when there was truly doubt (that they sanctified it based on evidence).
Even if it were said that this was a rule in the Great Law, the basic premise of the Gemara was that when there is no doubt, it is possible to cancel the second Yot Sheni, but that they should be careful in the custom of your ancestors lest the matter return to its defilement. According to my historical calculation, the sending of the matam is not in the Great Law (if it were in the Great Law, they would sanctify it based on evidence, and there was real doubt).
Rashi explained that lest the matter return to its defilement Let the secret of the sabbath be forgotten (and they will return to sanctification according to the evidence).
Nowadays, even if the matter were to be corrupted again, the Diaspora would know very quickly when they sanctified the month, and they would not need emissaries to go for several weeks to announce when the month was sanctified,
Therefore, there is no reason today for a second Yom Tiv (since there is no fear that the matter would be corrupted again), and there is a reason for two good days of Rosh Hashanah, for exactly the same reason as the Gemara - lest the matter would be corrupted again, and they would not be able to send a WhatsApp message on Rosh Hashanah to announce that the month was sanctified.

The Gemara makes it clear that this is a rule and not just a satisfactory practice. Regarding Reh, there is a Rishonim method that does not require two days.

A. Where is such a Gemara? After all, this is the subject of the assumption of the Eruvi Tevshilin and Eruvi Techumim, who argue that one of them is a day of rest.
B. Even if you find such a Gemara, I have already addressed it and written that it is explained in the Gemara that in practice Yot Shani would have been appropriate to be canceled if it were not for the words “be careful in the custom of your ancestors,” and this statement was certainly not stated in the Great Council.
C. Regarding Rosh Hashanah, there are indeed Rishonim who make light of this in the Land of Israel, and I have not understood their reasoning; abroad, there is no one who makes light of this.
And the Darna is for the Dina that there is a reason for Rosh Hashanah at this time, at least abroad, and not for the rest of Yot Shani.

Regarding the Rebbe, we discussed that it is one sanctification, and it is proven by the Hadith that it is a regulation. And regarding the rest of the 19, the things are explained in the Bitzah issues (this is how the whole issue goes. There too, they disagreed whether it is one sanctification or two, and this is not just a discussion of the laws of spikot). When I talk about a regulation, it is not necessarily in the Sanhedrin but in the Talmud, which has a law like the Great Council. Be careful, the custom of your ancestors is at most the reason for the regulation (like the Temple being built soon, which is also the reason for the regulation, and therefore even if it is invalid, it does not mean that the regulation can be canceled).
And see the things explained in the Rambam, in the Kiddush of the Month, 5:55, and in the Yom 1:12.
Although I wrote in the trilogy that there is room to cancel regulations that, due to the cancellation of the reason, have become obsolete and do not belong at all.
And regarding a message in the Lord, there is no problem sending a WhatsApp message on YouTube if they have made a promise and sent messengers on Shabbat. Therefore, there is no point in these regulations at all nowadays, and the situation will not return to normal.

In the Sefer Hatanya (Igeret Hakodesh, 26), it is explained that the second day of exile is not only a reminder of the need for alms during the holy month, but also carries a special divine light that is not revealed on the first day:
“And behold, the second day of exile has an advantage over the first day, being an addition of light from a higher level” – that is, it is an additional divine revelation and not just a technical regulation.
Likewise, in Lakutei Torah (P’Amor, D’Veh ve Krib’tam Asha) it explains that the second day of exile is connected to a special spiritual enlightenment that came as a result of the delay in exile:
“The second day of exile is a light that is delayed from descending on the first day and shines on the second day” – which clarifies the necessity of the day even when there is apparently no technical need for it.

Not only is the second day of exile relevant, but it expresses a deeper connection to holiness, especially in a generation of hiding one’s face. In the books of Hasidism, it is explained that the exile itself created tools for receiving a higher light on these days, and therefore its abolition for a mere “rational” reason reveals a lack of understanding of the spiritual nature of the custom.
Ignoring the kabbalistic foundations of Yom Tov Sheni and making it ”irrelevant” reflects a superficial approach to Jewish heritage. Beyond simple halacha, this day serves as a tool for discovering a higher divine light, as explained in the teachings of Kabbalah and Hasidism. Only someone blind to the spiritual level of the commandments could claim that it is unnecessary.

Obviously. In the book Likuti Amrei I expanded on this by saying that the second Yot is also meant to prevent obesity, beautify the body, and increase wealth, as well as to establish peace among the swans in the sick lake. Only someone who is blind to these theses could think that it is only meant to add divine light.