Deuteronómio 6:25 Midrash: Ein Yaakov (Glick Edition), Devarim Rabbah & Sifrei Devarim

"Who is greater than Moses among all Israel, who was attended at his death by God himself, as it is said (Deut. 34, 6) And He buried him in the land of Moab, opposite, Beth-Pe'or, etc. (Ib. 6, 25) And the Lord said unto us, 'Let it suffice thee.'" Said R. Levi: With the word Rab did Moses inform others, [of grave tidings.] And with the word Rab he himself was informed [of grave tidings]; i.e., with the word Rab did he inform others, as it is written (Numb. 16, 7) You assume too much [Rab] ye sons of Levi, and he was in turn informed by the word. And the Lord said unto me, '(Rab lack) let it suffice thee:' in another way may Rab be explained, thou hast a Rabbi whose name is Joshua. Still in another way may Rab be explained. Let it suffice to thee so that people should not say, "How rigorous the teacher [Lord] is and how persistent is the scholar." And why did the Lord act so rigorously against Moses? In the academy of R. Ishmael it was explained: According to the camel is his load [the greater the man the greater is his responsibility]. (Deut. 31, 2) Moses said unto them: 'I am one hundred and twenty years old today.' He need not say today, [if there is no special significance]. What does he mean by the word to-day? This means that today have my days been completed; from this we may infer that the Holy One, praised be He, grants the righteous the fulfillment of the years of their life to the very month and day, as it is said (Ex. 23, 26) The number of thy days will I make full. (Deut. 31, 2) I am not able any more to go out and come in. What does that mean, to go out and come in? Shall we take it literally? Behold it is written further (Ib. 34, 7) And Moses was one hundred and twenty years old when he died; his eyes were not dimmed, and his natural strength has not abated, and again it is written (Ib., ib., ib.) And Moses went up from the plains of Moab to the Mount of Nebo. Concerning which we are taught in a Baraitha the following explanation: There were twelve stairs to the Mount and Moses surmounted them all in one step. [Hence we see that Moses was healthy and strong up to his death?] Said R. Samuel b. Nachmeni in the name of R. Jonathan: "To come forth, refers to the discussions of the Torah, from which it may be inferred that the wellsprings of wisdom were shut up for him." (Ib. 13, 14) Moses and Joshua went and placed themselves in the tabernacle of the congregation. We are taught that that particular Sabbath was a Sabbath of Transmittance of office by two. The office was taken irom one (Moses) and given to the other (Joshua). [Hence both served on the same day].

Another matter, the Holy One blessed be He said: ‘If you read the Torah, you are performing a mitzva for the sake of My world, as were it not for the Torah, the world would have been restored to emptiness and disorder.’
Another matter, “for the mitzva” – what is “the mitzva”? The Rabbis say: It is a hard matter. To what is the matter comparable? It is to a king who had a gem and he entrusted it to his friend. He said to him: ‘I beseech you, pay attention to it and guard it properly, as if it is lost, you do not have anywhere from which to repay me, and I do not have another one like it. The result will be that you will have sinned against me and against you. Instead, perform the mitzva on behalf of both of us, and guard it properly.’ So, Moses said to Israel: ‘If you observe the Torah, you will not only be acting charitably [tzdaka] for yourselves, but for Me and for you, as it is stated: “It will be, therefore, to our merit [tzdaka]” (Deuteronomy 6:25) – for Me and for you.’ When? “[It will be, therefore, to our merit…] if we observe to perform all this mitzva” (Deuteronomy 6:25).

"He did the righteousness (tzedakah) of the L-rd": What kind of tzedakah did he do with Israel? All the forty years that Israel were in the desert, the well (of Miriam) rose up for them, and the manna descended for them, and the quail abounded for them, and the clouds of glory surrounded them! But (the tzedakah was that) he taught Torah to Israel, viz. (Devarim 6:25) "And it shall be (accounted) tzedakah to us if we observe to do all the words of this Torah."