Jamieson, Fausset and Brown on Exodus 6:3

3. I ... God Almighty--All enemies must fall, all difficulties must vanish before My omnipotent power, and the patriarchs had abundant proofs of this.

but by my name, &c.--rather, interrogatively, by My name Jehovah was I not known to them? Am not I, the Almighty God, who pledged My honor for the fulfilment of the covenant, also the self-existent God who lives to accomplish it? Rest assured, therefore, that I shall bring it to pass. This passage has occasioned much discussion; and it has been thought by many to intimate that as the name Jehovah was not known to the patriarchs, at least in the full bearing or practical experience of it, the honor of the disclosure was reserved to Moses, who was the first sent with a message in the name of Jehovah, and enabled to attest it by a series of public miracles.