In Rav Shailat’s edition of Rambam’s letters, (page 410) there is a letter to a simple Baghdad Jew, not a scholar. I already posted about a touching comment Rambam makes to this simple Jew http://yediah.blogspot.com/2007/04/was-rambam-elitist.html . Here is another part of this letter that opens up quite a vista about how Rambam viewed Torah and Mitzvot. The particular subject the letter deals with in this segment is repeated in Rambam’s Pirush Hamishna Chulin 7:6. Here is a translation/paraphrase as usual.
“You mentioned too, that people took exception with our statement that Mila (circumcision) was commanded by Moshe Rabbeinu and not our father Avraham. They argued that [I must be wrong] as the 13 covenants were made with Avraham. Whoever said this says a foolish thing and proves that he knows nothing about the foundations of the Law, while our statement is correct without a doubt. For among the 613 Mitzvot given to Moshe at Sinai, Mila and Gid Hanashe [the sciatic nerve which was forbidden based on the story of the fight between Yaakov and the angel] are included. It is as the Rabbis taught [in the Mishna Chulin 7:6], it was written in its place [as part of the story told in Chumash] but we follow the rule because it was given at Sinai that confirmed to us the prohibition of Gid Hanashe and [the mitzvah] of Mila which preceded it. As far as the 13 covenants mentioned at Mila [that apparently was the basis of the contention], it behooves to ask these blind people who are trying to compete with seeing men, the following question. Were those verses about the 13 covenants told to Avraham, written down and published by him and then Moshe Rabbeinu copied these verses and inserted them into the Torah as plagiarists do with the writings of others, or rather, the verses mentioned in the Torah were written by Moshe as he heard them from God? For anyone who does not believe that these verses including the whole Torah was told to Moshe from the mouth of God [literally – Hagevurah - the Power] is considered among those who claim the Torah is not from Heaven. How else would we know, and how did Moshe Rabbeinu know, what was told to Avraham when he was commanded to do Mila? We know it from Moshe at Sinai! Therefore, the source of this Mitzvah and its command is from Moshe Rabbeinu as are the 13 covenants, as told to him by God. This is obvious and is obscure only to one who has not learned the foundations of the law, wasting his days with the branches. There is no difference within parts of our Torah; the Torah commanded to us by Moshe, all of it comes from Moshe and Hashem. Everything that is in it that was given to an earlier person, such as the seven Mitzvot to Noach and Mila to Avraham we do not accept it because its earlier transmission but only because of the last command that was given to us, the community of Yaakov.”
Rambam offers a similar argument in his Pirush Hamishna on Chulin 7:6. Basically, the obligation that we have in keeping the Mitzvah of Mila stems from Sinai and not from the earlier command to Avraham. The same goes for the seven Noachide laws and Gid Hanashe, the obligation stems from Sinai and not the earlier revelation. The basis for this position is the Mishna in Chulin that sets this out regarding Gid Hanashe and Rambam extrapolates to all other similar Mitzvot. The theology underlying this is the uniqueness of Moshe’s prophecy and Rambam in MN 2:39 expands on it.
“There were prophets before Moses, as the patriarchs Shem, Ever, Noah, Methuselah, and Enoch, but of these none said to any portion of mankind that God sent him to them and commanded him to convey to them a certain message or to prohibit or to command a certain thing. Such a thing is not related in Scripture, or in authentic tradition. … Men like Abraham, who received a large measure of prophetic inspiration, called their fellow men together and led them by training and instruction to the truth which they had perceived. … Abraham did not tell the people that God had sent him to them with the command concerning certain things which should or should not be done. Even when it was commanded that he, his sons, and his servants should be circumcised, he fulfilled that commandment, but he did not address his fellow men prophetically on this subject.”
I would also like to touch on two other rather revealing statements in this letter. When Rambam argues “Were those verses about the 13 covenants told to Avraham, written down and published by him and then Moshe Rabbeinu copied these verses and inserted them into the Torah as plagiarists do with the writings of others?” he rejects any possibility of a documentary basis for torah. IOW, according to him, he would have considered plagiarism were the Torah to quote an earlier source and not refer to it as such. Absent a clear reference, we must assume that the source was revelatory only. It does not negate the possibility of a written record by Avraham; it just does not accept it as a source. When Rambam asks “How else would we know, and how did Moshe Rabbeinu know, what was told to Avraham when he was commanded to do Mila?” he is saying that the Torah is telling the story its way and from its perspective. The historical record is much less important than the interpretation thereof.
The other comment I find fascinating is “This is obvious and is obscure only to one who has not learned the foundations of the law, wasting his days with the branches.” Rambam sees the Torah as a tree with roots, a trunk and branches. The roots contain the basic theology and the trunk is the corpus of philosophy and laws that grow out of those roots. How to perform the Mitzvot in detail are the branches. Focusing on the branches alone is like seeing the trees without the forest. (I know, at least I think I know, Rambam uses this metaphor “Shoresh and Anaf” in a similar context elsewhere. I, for the life of me, cannot think where. I could use some help.)
 יד עַל-כֵּן, יֵאָמַר, בְּסֵפֶר, מִלְחֲמֹת יְהוָה: אֶת-וָהֵב בְּסוּפָה, וְאֶת-הַנְּחָלִים אַרְנוֹן. 14 wherefore it is said in the book of the Wars of the LORD: Vaheb in Suphah, and the valleys of Arnon, (Bamidbar 21:14)