If a person believes with certainty in X, then of course there is no doubt that one can say he should do what he believes.
But here, obviously, we enter the dimension in which the person himself is unsure what the “truth” is, and so the question arises what he should do in that situation. The best he can do under uncertainty.
Indeed, I am not sure the considerations here would דווקא be value-based considerations, because they are partly located in the percentage of meaning as opposed to the parallel sort of nihilism.
If so, the considerations have to be external considerations (say, pragmatism?). But some of those considerations, like pragmatism, are not valid in a world where there is no possible Hell, a world that, to the best of my knowledge, the Rabbi somewhat supports.
And therefore, I am interested in hearing your learned opinion on the matter. Is “for its own sake” enough for a suffering person who is in doubt?

B. I would be glad to hear your response to the question: is the statement that life has meaning a prescriptive statement or a descriptive one?
That is, is the existence of meaning a neutral fact, while values are what pour the evaluative dimension into it, or is it itself a statement with evaluative content?
C. As for the content of meaning: that a person is born against his will is obvious, but of course he has the choice not to die against his will; that is what the mishnah says earlier in the first chapter: “And do not let your inclination assure you that the grave is a place of refuge for you” … and only afterward, “and whether you like it or not, you die” … and the prohibition neither adds nor subtracts; if anything, it only weakens and diminishes the option for the believing person and his inclination in that regard.
In any case, already in those words, “from here on, examine your deeds,” one can interpret this in the Jewish conception of the importance of deeds 🙂 So from your perspective the meaning of life is the classic one that emerges from your writings: morality + Torah and commandments.
Is there also, in your toolbox of ideas, a place for self-realization, building the soul? Building the intellect in the philosophical sense? Or attaining happiness in the New Age sense? Or only service for a higher purpose, in a kind of Kabbalistic Age sense?

By the way, the question being asked comes partly from my own curiosity about this topic, but also because I am speaking with someone who asks things in this style, and I think it is proper to hear the person from a place of understanding and prior theoretical reflection, and that is enough said… And one can sharpen it by noting that you understood this from the phrase “let him do what he believes,” precisely.

I am sorry, but I truly do not understand the question. As I wrote, I do not understand what “meaning” is. It is a vague word and has a psychological connotation (and therefore is not relevant). Does he think there is a divine command? Is there an obligation to obey it? Then that is that. No command, or no obligation? Then certainly there is nothing to do.
If you are asking about a person who is unsure whether there is or is not a command, then here again it depends on his standards: what level of certainty is required for him to act. I do not understand the question, and even regarding what I do understand, I do not know how to answer such undefined questions.

In difficult cases, it is worth starting by being precise about the terms.

Meaning is something emotional. Life is a phenomenon in reality. And just as an electron has no emotion and no meaning, so life has no emotion and no meaning.
The one who has meaning, or who lacks meaning, is the person. Not life.

And like any other emotion, the person needs to try to clarify why he feels the way he feels.

And as I have remarked in other threads, “the question of the meaning of life” is a question in psychology, not a question in philosophy.

And one can summarize and say that there are two kinds of things that fill a person: things that happened to him in the past, or goals that a person has for the future.

If he has neither of those two, the person will feel a lack of meaning.

Of course we are talking about a state of doubt and not a binary situation; the point that you do not know what is most correct to do in these matters is exactly my question…. If it were clearly explicit, then there would be no room for my question here, I hope…

On the possibility that there is meaning and no continuation, that is, everything is in the category of “for its own sake” — does that have the power to overcome inclination and suffering?
Seemingly this is a classic conflict between inclination and value, but here the value is uncertain, so methodologically it does not necessarily override the inclination.