It is important to observe the distinction between the two verbs. Abraham's life was under the conditions of time, and therefore had a temporal beginning. Hence, Abraham came into being, or was born (γενέσθαι). Jesus' life was from and to eternity. Hence the formula for absolute, timeless existence, I am (ἐγώ εἰμι). See on Joh 1:3; see on Joh 7:34.