1.  It is the Spirit himself who withdraws his influence after a period of constant reproofs were graciously made to a man and yet that man refuse to believe because of pride. Heb.10: 26 says, "For if we sin willfully after that we have received the knowledge of the truth, there remaineth no more sacrifice for sins...Of how much sorer punishment, suppose ye, shall he be thought worthy, who hath trodden under foot the Son of God, and hath counted the blood of the covenant, wherewith he was SANCTIFIED, AN UNHOLY THING, AND HATH DONE DESPITE UNTO THE SPIRIT OF GRACE?" (Heb.10:26,29).  Despite means INSULT. So after the Spirit has graciously dealt with  him, and he persistently refused and mocked Him, the Spirit  will give him up. (Rom.1;21-28; Prov.1:23-32).

2. In the case of Saul, he had intellectually learned God's Laws. He had been exposed to Christians as he sought to persecute them. The Spirit must have started to deal with him as he saw how Christians reacted to his persecutions. Many Christians whom he persecuted must have constantly prayed for him. The loving and godly reactions of Christians whom he persecuted demonstrated the grace of God to him, and the more he pushed the Christians, greater grace bounced back.  The prayerful afflicted Christians moved the Spirit to bestow greater grace on Saul, until it came to a point where he met Christ personally.  After a long time confusion and struggle in his heart (such confusion caused him to do wrong), he encountered Christ. The Bible says that Saul was zealous in the wrong way. He thought he was serving God. He had many knowledge of the Scriptures. I think he believes in God. He came in contact with faithful Christians when he sought to persecute them. So I believe there is a volume of grace bestowed on Saul as God's purpose were conditioned upon those mentioned factors. So, When he encountered Christ, he said "Who are you, Lord?" Such is a humble inquiry of who the Lord really is. He was trembling when he learned it was Jesus and such demonstrated fear after knowing who Christ is. And he said, "Lord, what do you want me to do?"(Acts 9:6). Such demonstrated humility.  So we can find these sequence in the life of Saul who became Paul:

Knowledge of who Jesus is -- Fear of God -- Humility -- Faith ( Titus 1:1).