Exodus 6:3

and I appeared unto Abraham, unto Isaac, and unto Jacob by the name of God Almighty, but by My name Jehovah was I not known to them. To the patriarchs the Lord had not revealed Himself in His specific capacity as Jehovah, although the name was not unknown to them. Now He wanted to give actual evidence, definite proof, of Himself in fulfilling His promises, in carrying out the conditions of the Messianic covenant, at least in its typical form.