Principle I. To know the existence of the Creator
To believe in the existence of the Creator, and this creator is perfect in all manner of existence. He is the cause of all existence. He causes them to exist and they exist only because of Him. And if you could contemplate a case such that He were not to exist then all things would cease to exist and there would remain nothing. And if you were to contemplate a case such that all things would cease to exist aside from the creator, His existence would not cease. And He would lose nothing and oneness and kingship is His alone. Hashem of strength is His name because He is sufficient with His own existence and suffices just Him alone and needs no other. And the existences of the angels, and the celestial bodies, and all that is in them and that which is below them all need Him for their existence. And this is the first pillar and is attested to by the verse "I am Hashem your God.
Maimonidies, Guide to the Perplexed i. 75
We do not call a human being weak because he cannot move one thousand hundred-weights, and we do not attribute to the God, may he be exalted, incapacity because He is unable to corpify his essence or create someone like Him or to create a square whose diagonal is equal to its Side
Maimonidies, Guide to the Perplexed, iii. 15
The impossible has a stable nature, one whose stability is constant and is not made by a maker; it is impossible to change it in any way. Hence the power over the maker of the impossible is not attributed to the deity. This is a point about which none of the men of speculation differs in any way … Likewise, that God should bring into existence someone like himself, or should annihilate Himself, or should become a body, or should change – all of these things belong to the class of the impossible; and the power to do any of these things cannot be attributed to God
Dispute on this principle
R’ Moses Taku
They are issuing a decree to the Creator as to how He must be. By doing so they are degrading themselves
R Nachman of Breslov (as reported by disciple)
"He mentions that it says in their [the philosophers] books "It is possible that a triangle can be a rectangle?" Our master said "I believe that God can make a rectangular triangle. For the ways of God are hidden from us; he is omnipotent, and no deed is bey him"
Notes of Marc Shapiro
Summary of principle
The first principle declares that God exists, that he is perfect in every way, and that he is the cause of the existence of all things. The principle also includes the belief that God is eternal, for he ‘an existent Being which is perfect in all aspects of existence’ and perfect existence precludes dissolution
Clarification of who agrees with Maimonides
Before Maimonidies, the above view was affirmed by Saadiah Gaon and R’ Ezra ben Solomon (Spanish mystic, died 1238)
Clarification on the nature of the dispute
The dispute between Maimonides and those who limit God is only over what constitutes the impossible, with Maimonides having a more restricted understanding of this than some other thinkers"
Clarification on the nature of the principle
1) Maimonides’ other point in this principle is that God is the casue of the existence of all things
2) This is not an assertion of creation ex nihlio
3) Establishes Gods ontological priority to the Universe. In other words the universe is dependent upon God for its existence
4) Possibility that the universe has coexisted eternally with God