And I appeared unto Abraham, unto Isaac, and unto Jacob, by the name of God Almighty, but by my name {a} JEHOVAH was I not known to them.

(a) By which he signifies that he will perform indeed that which he promised to their fathers: for this name declares that he is constant and will perform his promise.

Jamieson-Fausset-Brown Bible Commentary

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.

Matthew Henry's Concise Commentary

6:1-9 We are most likely to prosper in attempts to glorify God, and to be useful to men, when we learn by experience that we can do nothing of ourselves; when our whole dependence is placed on him, and our only expectation is from him. Moses had been expecting what God would do; but now he shall see what he will do. God would now be known by his name Jehovah, that is, a God performing what he had promised, and finishing his own work. God intended their happiness: I will take you to me for a people, a peculiar people, and I will be to you a God. More than this we need not ask, we cannot have, to make us happy. He intended his own glory: Ye shall know that I am the Lord. These good words, and comfortable words, should have revived the drooping Israelites, and have made them forget their misery; but they were so taken up with their troubles, that they did not heed God's promises. By indulging discontent and fretfulness, we deprive ourselves of the comfort we might have, both from God's word and from his providence, and go comfortless.