Let us ponder this commandment for a moment.

Is the first commandment a commandment - or is it, as it reads simply, a statement of G-d's existence - and an introduction to the commandments?(16)

It is a commandment. I am your G-d is to be defined as Believe in me, Your G-d (or, inversely, Do not deny My Existence).

Let us understand.

If Torah is the key to bringing the world to perfection it must be because Torah itself is an expression of perfection. If this commandment is not stated explicitly there must be a reason why it could not have been explicitly stated.

What is that reason?

Let us observe the difference between the first commandment and the nine commandments that follow it.

The nine commandments that follow are of an instructive nature. G-d instructs Man to (or not to) act. Implicit in these commands is that Man, the actor, retains the ability to disregard G-d's command.

A commandment orders Man to choose an option.

The first commandment can not be said in command form: Make me your G-d: Believe in Me - because G-d's Divinity is not dependent on the choice of Man.

The belief in G-d can only be expressed as a statement.

"I am Your G-d," G-d says.

Our obligation is to see that this statement is true in our minds.

Also, consider: Religious commandments are commands because they are the order of a Being previously identified as Commander; the command of an entity already accepted as G-d. There is no possibility of a previously not accepted G-d commanding a people to believe His Divinity. Thus, G-d could only express the command to believe in His Divinity as a statement of His existence.

15 Tiferes Yisroel; chapter 37

16 Nachmanadies presents the opinion that this sentence is indeed an introduction to the Ten Commandments. Accordingly, the sum of Ten Commandments is reached by the second commandment being comprised of two different commandments.