In John 8:58, the Lord proclaimed to his listeners and those through the ages, “Jesus said unto them, ‘Verily, verily, I say unto you, before Abraham was, I am.’”
He is and always has existed. This statement showed that unlike Abraham, who had a beginning, the Lord is eternal, without beginning or ending. The words used by the Lord are as God used when Moses asked him what he should tell the children of Israel when they would ask, “What is his name?”
“And God said unto Moses, ‘I am that I am,’ and he said, ‘Thus shalt thou say unto the children of Israel, I am hath sent me unto you’” (Exodus 3:14). Jesus was in the beginning with God (John 1:1-14). He is deity.
This claim by the Lord was not given by itself. It came after a lengthy discussion of his being, his offer of salvation and his knowledge of Abraham.
If the Jewish leaders of Jesus’ day had studied and believed the prophets, they would have known Jesus was the messiah. Instead of embracing him as the Son of God, they — scribes, Pharisees and Sadducees — tried to discredit him in any way possible.
In John 8, the scribes and Pharisees believed they had found the perfect way of destroying his credibility with the people. They brought to Jesus a woman caught in the act of adultery. They reminded Jesus what the Law of Moses taught: The woman should be stoned. However, to stone a person would have violated the Roman law at that time, as only a judge could put someone to death. If he denied the teaching, the people would lose the respect for him; if he upheld the law, the Romans would have gotten involved.
Jesus did not give a direct answer. He just stooped down and began writing on the ground, as if they were not even speaking to him. When he stood, he said, “He that is without sin among you, let him first cast a stone at her.” Then, he stooped and wrote on the ground again. None of the accusers still were present when Jesus stood up the second time. He defeated his adversaries by appealing to their consciences. They realized their own situation and could not execute judgment upon the woman.  
Those who remained still tried to discredit Jesus. When he proclaimed he was the light of the world and those that followed him would have “the light of life,” they told him his record was not true. They had not understood his meaning when he said those words earlier. The Father bore witness of him, for Jesus knew he was of the Father.
Their problem was that they only thought they knew the Father. Jesus actually pointed out to them that they did not know the Father, because they did not know him (John 8:19). Their prejudice blinded them to the truth of what they should have known if they truly were following God. The religious leaders were rejecting salvation offered to them by God.
This was a fulfillment of the prophecy of Zachariah 11. Those who should have been leading the people to God were leading them astray, as the rest John 8 reveals.
Jesus came to Earth and took the form of a servant (Philippians 2:6). He freely gave himself for all mankind to have the opportunity of salvation — if they would obey the Gospel.

This is part one of a two-part series.