Yesodey haTorah

As he states in his introduction, the Rambam intended the Mishneh Torah to explain all the various mitzvot which we are obligated to perform. Nevertheless, rather than discuss each mitzvah individually, he has grouped several mitzvot together and explains them in the same halachah. In order to clarify which mitzvot are discussed in each of the halachot, he lists them at the very beginning.

1. Note that the Rambam uses the word "to know", and not "to believe". The popular translation of Sefer HaMitzvot (the Rambam himself composed the text in Arabic, the Mishneh Torah being the only text he wrote in Hebrew) begins: “The first mitzvah is the commandment... to believe in God.”

Many other Sages have objected to the latter definition of the commandment. For example, in his text Rosh Amanah, Rav Yitzchak Abarbanel mentions two frequently asked questions:

a) How can the first commandment be to believe in God? He is the one who issued the commandments. Without belief in Him, there can be no concept of serving Him by carrying out His will.

b) How can one command belief? Belief is a state of mind and not an action that is dependent on a person's will.

By stating that the command is "to know" - i.e., to develop one's knowledge and awareness of God - both of these questions are answered: Though one believes in God, he must work to internalize that belief and make it part of his conscious processes. Furthermore, the intellectual activity necessary for this process of internalization is an act which can be required of a person. See Derech Mitzvosecha, mitzvas HaAmanat Elokut.

[Note also the Hasagot of the Ramban to Sefer HaMitzvot and the response of the Megillat Esther. Also, it is worthy to mention that Rav Kapach and other modern translators of Sefer HaMitzvot also translate the command there as "to know."'