Albert Barnes Commentary Exodus 3:13

"And Moses said unto God, Behold, when I come unto the children of Israel, and shall say unto them, The God of your fathers hath sent me unto you; and they shall say to me, What is his name? What shall I say unto them?" — Exodus 3:13 (ASV)

What is his name - The meaning of this question is evidently: “By which name shall I tell them that the promise is confirmed?” Each name of the Deity represented some aspect or manifestation of His attributes (compare the introduction to Genesis). What Moses needed was not a new name, but direction to use that name which would bear in itself a pledge of accomplishment. Moses was familiar with the Egyptian habit of choosing from the names of the gods the one that had particular relevance to the needs and circumstances of their worshippers, and this may have suggested the question he anticipated his own people would ask him first.