halacha - Is belief in a G-d a commandment?

I am studying to convert to Judaism and one of the questions I was asked was about the Ten Commandments. I remember reading at that time that there was debate about the division of the statements Moses brought down on tablets and that they are, in Hebrew, more commonly called the "Ten Statements" than the "Ten Commandments." I am particularly interested in the "first" and whether or not it is considered a commandment to believe in G-d. After all, how can a person be commanded to have a particular belief?

Answer

Belief in God cannot possibly be a commandment.

A commandment is something one fulfills because he already believes in the one who is commanding it. Thus, a commandment to believe in the existence of the commander is an absurdity; it assumes in its fulfillment that it has already been fulfilled. (This argument was presented by R' Hasdai Crescas.)

For this reason, many Rishonim did not count those first few words of the ten statements - "I am the LORD thy God, who brought thee out of the land of Egypt, out of the house of bondage" - as a commandment, but rather as an introductory line to the entire monologue. [There is a Talmudic statement, though, that the first two commandments came from God directly, and they are identified as the first two statements of the ten. How to count those two commandments is a discussion in itself.]

Now, what to make of the Rambam, who counted belief in God as the first commandment, and tied it to this first verse of the ten commandments? The answer is proposed by Abarbanel in Rosh Amanah as follows:

The commandment is not belief in God, but rather the belief that God has certain qualities, namely that He is independent of all other existences and that all other existences are dependent upon Him. This is evident from Rambam's description of this mitzva in the Mishna Torah (Hil. Yesodei Hatorah 1:1-3) (my own translation):

יסוד היסודות ועמוד החכמות לידע שיש שם מצוי ראשון והוא ממציא כל נמצא וכל הנמצאים משמים וארץ ומה שביניהם לא נמצאו אלא מאמתת המצאו. אם יעלה על הדעת שהוא אינו מצוי אין דבר אחר יכול להמצאות. ואם יעלה על הדעת שאין כל הנמצאים מלבדו מצויים הוא לבדו יהיה מצוי ולא יבטל הוא לבטולם שכל הנמצאים צריכין לו והוא ברוך הוא אינו צריך להם ולא לאחד מהם לפיכך אין אמתתו כאמתת אחד מהם.

The cornerstone of cornerstones and the pillar of all wisdoms is to know that there is a first existence who brought into existence all existences, and all existences, the heavens and Earth and all that is in between would not exist without the truth of his existence. If it enters the mind that He does not exist, then nothing else is able to exist. And if it enters the mind that nothing else besides Him exists, then He alone will exist and He will not cease because they have, for all existences require Him and He, blessed is He, does not require them, nor any one of them. Therefore, His reality is not like theirs.

A more detailed description of this idea can be found in the first of Rambam's thirteen principles. Essentially, the commandment is that we should believe that God, whom it is already assumed that we believe in His existence, possesses the above qualities.

What about the fact that I cannot command someone to believe something? A person believes what he believes; he cannot be forced. To this Abarbanel responds that the commandment is not to actually believe, but rather to contemplate. We are commanded not to blindly follow faith, but rather to strive toward knowledge and to weigh it approprately to come to the conclusion that the above is true. (Admittedly, I don't fully understand this concept, but it seems that given the information that is available to us and our traditions, it is reasonable that we come to the correct conclusion.)

See this article for more information.