Acts 22:14
And he said, The God of our fathers hath chosen thee, that thou shouldest know his will, and see that Just One, and shouldest hear the voice of his mouth. And he said, The God of our fathers hath chosen thee, that thou shouldest know his will, and see that Just One, and shouldest hear the voice of his mouth.
God chose Paul to know His will, to see Jesus as the Just One and risen Christ, and to hear the voice of His mouth. That divine choice brought his proud heart to bow before the crucified Nazarene. This preparation fitted him to witness to all people concerning what he had seen and heard. By that divine will he was made to serve as an apostle.
His mission to the Gentiles was not his own choice, for though he wanted to labor for his own people, God directed him in a vision in the temple to carry the message to the Gentiles.
His encounter with Jesus and conversion enabled him to preach that Jesus is the Son of God. The divine light given to him after his conversion illuminated the prophecies about Jesus, enabling him to show from Scripture that Christ's first advent, sufferings, death, and resurrection were foretold.