Rambam: Shemot: What Is His Name? Part Two
Moreh Nevuchim – Guide To The Perplexed, Section I, Chapter 63 continuation: When God appeared to our Teacher Moses, and commanded him to address the people and to bring them the message, Moses replied that he might first be asked to prove the existence of God in the Universe, and that only after doing so he would be able to announce to them that God had sent him. For all men, with few exceptions, were ignorant of the existence of God; their highest thoughts did not extend beyond the heavenly sphere, its forms or its influences. They could not yet emancipate themselves from sensation, and had not yet attained to any intellectual perfection.
Then God taught Moses how to teach them, and how to establish amongst them the belief in the existence of Himself, namely, by saying Ehyeh asher Ehyeh, a name derived from the verb hayah in the sense of” existing,” for the verb hayah denotes to be,” and in Hebrew no difference is made between the verbs” to be” and” to exist.” The principal point in this phrase is that the same word which denotes” existence,” is repeated as an attribute.
The word asher,” that,” corresponds to the Arabic illadi and illati, and is an incomplete noun that must be completed by another noun: it may be considered as the subject of the predicate which follows.
The first noun which is to be described is Ehyeh: the second, by which the first is described, is likewise Ehyth, the identical word, as if to show that the object which is to be described and the attribute by which it is described are in this case necessarily identical. This is, therefore, the expression of the idea that God exists, but not in the ordinary sense of the term: or, in other words, He is” the existing Being which is the existing Being,” that is to say, the Being whose existence is absolute. The proof, which he was to give, consisted in demonstrating that there is a Being of absolute existence that has never been and never win be without existence.