God said to Moses, “I AM WHO I AM. This is what you are to say to the Israelites: ‘I AM has sent me to you.’”
14. I am that I am. The verb in the Hebrew is in the future tense, “I will be what I will be;” but it is of the same force as the present, except that it designates the perpetual duration of time. This is very plain, that God attributes to himself alone divine glory, because he is self-existent and therefore eternal; and thus gives being and existence to every creature.
God, having spoken to Moses, allows him also a liberty of speech, which he here improves; and, I. He objects his own insufficiency for the service he was called to (Exo 3:11): Who am I? He thinks himself unworthy of the honour, and not par negotio - equal to the task.
Commenting on Exodus 3:11-15
And God said unto Moses, I am that I am,.... This signifies the real being of God, his self-existence, and that he is the Being of beings; as also it denotes his eternity and immutability, and his constancy and faithfulness in fulfilling his promises, for it includes all time, past, present, and to come; and the sense is, not only I am what I am...