In John 8:57, the Jews wanted Jesus to answer how it is possible for Him to preexist to the time of Abraham, who lived 1800 years ago, yet He is less than 50 years old. Jesus already claimed preexistence in John 8:56, because He said He met Abraham. So John 8:58 must be much more than claiming preexistence. So Jesus answers the Jews' question, but not in the way they expected Him to. He says, "Before Abraham was born, I am" and the Jews wanted to kill Him for saying that. Why? Because He claimed preexistence for the 2nd time? No.

Jesus told them, He has met Abraham and Abraham has seen Him, because He is YHWH, the one who appeared to Abraham in Genesis 18:1 and other OT places.

If Jesus was claiming deity, would the Jews' response in John 8:59 make perfect sense? Of course. If Jesus was merely claiming preexistence, would the Jews consider that blasphemy and worthy of death? No. Claiming to be very old is not blasphemy. And no angel can say what Jesus said in John 8:58. Only YHWH can. Jesus specifically said "I am", the unique title of Jehovah. He deliberately doesn't say, "I was", or "I existed" or "I have been". This is very significant. The Jews response in John 8:59 would be an extreme overreaction if Jesus was claiming anything other than deity.

Jesus says, "before a creature came into being, I eternally exist in the perfect present tense". Abraham had a beginning, but Jesus is contrasting Himself to Abraham, who is a creature. Jesus is saying He had no beginning; He is eternal - He is NOT a creature. Hence, the Jews' desire to kill Him, because YHWH alone is eternal, uncreated.