Terence Fretheim is spot on when he says, “Exodus 3:14 is one of the most puzzling verses in the OT.” But since fools go where angels fear to tread, I’ll proceed.
It seems to me the place to start is with Moses’ question, “Suppose I go to the Israelites and say to them, ‘The God of your fathers has sent me to you,’ and they ask me, ‘What is his name?’ Then what shall I tell them?” (3:13). Moses is asking for more than just a combination of letters to pass along to the Hebrews. He wants more than a password. He seems to be asking for some self-revelation from God that is in keeping with the mission he is being given.
This isn’t really outside our experience. If someone tasks us with something special, don’t we expect some inside information from them? Maybe we are looking for something of their reasons for the assignment, what they hope to accomplish, how it fits into the bigger picture, etc. It’s certainly not outside Israel’s experience as we see God deal with Abraham (Genesis17:1ff) and Jacob (Genesis 35:9-14) in this manner. So there was precedent for Moses’ request of God. In fact, maybe that’s what Moses is implying in his question of v. 13—“You revealed Yourself to the fathers, what ‘name’ will You give to me?”
God’s response, translated by the NIV as “I AM WHO I AM,” is capable of being understood a few ways. The marginal reading offers, “I WILL BE WHAT I WILL BE.” Fretheim suggests, “I will be who I am/I am who I will be.” In all of this, the context gives us a couple of directions to choose from. We can go with a translation that reinforces the burning bush—that God is self-existent and depends on no one (symbolized by the bush burning but not being consumed). Or, we can go in the direction that God is condescending to Moses’ request and revealing something about Himself to provide reassurance to him and Israel (see v. 16-17).
This is not exactly a trivial point about some obscure Hebrew words, it is about understanding the phrase that becomes the basis for the name God reveals Himself by (v. 15)—a name that is used almost 7,000 times in the Old Testament. For this reason, I lean toward the Fretheim’s ”I will be who I am/I am who I will be.” With these words, God is doing more than affirming His self-existence (something very important), He is promising His faithfulness—which seems most relevant to the circumstances and in keeping with v. 16-17. And as others have pointed out, because of Yahweh, Israel becomes the bush that burns under trial but is not consumed.
What does Exodus 3 tell us? God, who had revealed Himself to the fathers as El Shadai (Almighty God), now adds something important to that. He is not only Almighty—He is faithful. He will be who He is. The One who made promises will not forget them or change in regard to them. When pressure is mounting and others are failing, He will be who He is.
That was good news for Moses and Israel and it’s good news for us.