How do you explain the wording, "who fed you with manna etc., in order to test you, to do you good in your end"? What is "doing you good in your end" if not reward at some point in time?

It could be in this world too (that is also the plain sense of the wording), especially in an era when there was still divine involvement in it. The gates of interpretation have not been locked.

Avodah Zarah 3a: Rabbi Yehoshua ben Levi said: What is the meaning of that which is written, "which I command you today"—today to do them, etc.

I could present another thousand such homiletic interpretations. The distance from that to a real source is very great.

Does the Rabbi not relate to the Sages as an authoritative source? Is the Rabbi expecting a source from the Hebrew Bible alone? I thought the Rabbi does accept their halakhic authority. Or does the Rabbi hold that in a derashah like this there is a departure from their authority?

I explained that there is no authority in the realm of facts, only in Jewish law. The question whether there is or is not a World to Come and reward is a factual one. In that, the Sages have no authority.

Is this a derashah? Even without accepting the authority of the Sages, there is a verse here from which the matter is inferred directly and precisely, and not through "forced readings." Does the Rabbi see a reading and precision in the verse as more correct than the way Rabbi Yehoshua ben Levi understood it? "Which I command you today to do them." Does the Rabbi agree that the Torah does not use unnecessary words? Then our conclusion is necessarily the reward, which is the consequence and accompaniment of the command.

How many other interpretations/homiletic readings do you want? This is merely an aggadic prooftext, and you have turned it, for no reason at all, into the plain meaning of the verse. That's actually amusing.
Today to do them — and not to postpone the doing to a later time.
Today to do them — while it is still day and not at night.
And so on.

It is possible that the Torah's promises of physical reward and punishment were directed to the generations before the stage of the hiding of the divine face ("And I will surely hide My face on that day"). A bit like a father who promises his child a reward when he is young if he listens to him. Obviously, when the child grows up, the promise of reward expires, because the child is expected to do as his father says even without reward, out of gratitude and recognition of the importance of the matter. The reward serves only as a temporary educational tool until the child reaches maturity.

Yes, I wrote that above.

The Rabbi brought examples of halakhic derashot. And since there are no such derashot in the world of Jewish law from the verse in question (right?), then they are not optional, correct? (Unless the Rabbi produces halakhic derashot directly from the verses.) So then how should the verse be read not in accordance with Rabbi Yehoshua ben Levi? And I was glad to read the Rabbi's words, "That's actually amusing," as it is written: "Had Your Torah not been my delight, I would then have perished in my affliction." And would that I might bring about the fulfillment of "from my students more than all of them" with respect to the Rabbi.

It is obvious that reward and punishment are literal—meaning, in this world. And whoever does not accept this denies the Torah of Moses.

NF,
I'm really not following you. A. The first derashah I brought is not halakhic. B. Even if it were—what is the problem? Anyone can interpret. C. Even if not everyone can interpret, the Sages could. D. Even if there is no derashah at all—why do we need derashot? We are talking about the plain meaning of the verse. Are there not plenty of verses/words for which we have no derashah?
In short, this is nonsensical as a source.

What does the Rabbi think about the other prophecies that explicitly hint at this, like in Daniel? Or in Psalms?

I have no position. Everything is open to interpretation, and it is hard to draw any unequivocal conclusion from the Bible.

In this verse we need a derashah, or peshat—I don't know what to call it—because of an apparently redundant word. Are there verses lacking derashot even when they called for interpretation? I don't think so. And even if you were to say so, still, just because there are places in the Talmud that remain unresolved, would we now leave all Talmudic topics unresolved? And similarly in matters of science, etc. So too here: just because there are places where we have not brought a plain explanation for a verse out of necessity, then where there is a choice should we choose not to explain the plain sense? Rabbi Yehoshua ben Levi offered a legitimate plain reading that arises from the basic need to understand a difficult verse without derashah. There is no strained question here and no strained answer according to Rabbi Yehoshua ben Levi. There is a necessary question here and a necessary answer, simply speaking.

Hi, I'm back. This time we'll go according to the order of the letters that the Rabbi arranged, for the reason for which the Rabbi arranged them by letters.
A. Indeed, in my view this is a halakhic derashah, since it touches on the manner of fulfilling the commandments, even though it is expounded rather generally.
B. In my opinion, not everyone can interpret. And if I dare, I would say that his opinion is also like mine.
C. The Sages could, but they did not do so in the present case.
D. Granted, it may be that there is no necessity for derashot (despite the common concept of PaRDeS), so let us call Rabbi Yehoshua ben Levi's peshat the plain meaning of the verse and not a derashah. And behold, dawn has broken on a source for reward in the World to Come.
May you be inscribed and sealed for a good year!

Read my words again. There is no source for this, aside from an aggadic midrash of the Sages. If they received it by tradition—of course I will accept it. But if not, the case has an answer.
May you, and all of us, also be inscribed and sealed for a good year.