John 8:58 - Ellicott's Commentary On The Whole Bible

Before Abraham was, I am. — Better, Before Abraham was born, I am. (Comp. Note on John 1:6; and see another striking instance in Luke 6:36, “Become ye merciful as your Father also is merciful.”) Here they ask in wonder, not unmixed with scorn, if He was coeval with Abraham. The answer is that Abraham, like all men, came into being. There was a time when he was not. But there was never a time when the Son of God was not. In the time before Abraham, in the eternity before time (John 1:1), He still was. No word which expresses becoming can be used of His existence. He is the I AM, present equally in the human “was,” and “is,” and “is to come.”