A.T. Robertson Commentary John 8:58

"Jesus said unto them, Verily, verily, I say unto you, Before Abraham was born, I am." — John 8:58 (ASV)

Before Abraham was (πριν Αβρααμ γενεσθα). Usual idiom with πριν in positive sentence with infinitive (second aorist middle of γινομα) and the accusative of general reference, "before coming as to Abraham," "before Abraham came into existence or was born."

I am (εγω ειμ). Undoubtedly here Jesus claims eternal existence with the absolute phrase used of God. The contrast between γενεσθα (entrance into existence of Abraham) and ειμ (timeless being) is complete. See the same contrast between εν in 1:1 and εγενετο in 1:14. See the contrast also in Ps 90:2 between God (ε, art) and the mountains (γενηθηνα). See the same use of ειμ in Joh 6:20; 9:9; 8:24,28; 18:6.