9:19b-20 How verses 19b-20 fit into the chronology of events in Saul's life is not perfectly clear. They could fit in any number of ways. We should probably understand "immediately"in a general sense. As soon as Saul became a Christian he began to contend that Jesus was the Messiah when he attended synagogue worship, which he did regularly (cf. 13:5, 14; 14:1; 17:2, 10, 17; 18:4, 19; 19:8). This proclamation was the result and evidence of his being filled with the Holy Spirit (v. 17) as well as the result of his conversion.
Saul later wrote that immediately following his conversion he did not consult with others about the Scriptures but went into Arabia and later returned to Damascus (Gal. 1:15-17). "Arabia"describes the kingdom of the Nabateans that stretched south and east from Damascus. Damascus was in the northwest sector of Arabia. After Saul's conversion and baptism he needed some time and space for quiet reflection and communion with God. He had to rethink the Scriptures, receive new understanding from the Lord, and revise his Pharisaic theology. So as Moses, Elijah, and Jesus before him, he retired into the wilderness.
This is the only mention in Acts of someone proclaiming Jesus as the "Son of God"(but cf. 13:33). This fact reflects the clear understanding of Jesus that Saul had even shortly after his conversion. As used in the Old Testament, this title referred to Israel (Exod. 4:22; Hos. 11:1), Israel's anointed king (2 Sam. 7:14; Ps. 89:26), and Messiah (Ps. 2:7). Saul recognized that Jesus was the Son of God predicted there. He used this title of Jesus frequently in his epistles (Rom. 1:3-4, 9; 5:10; 8:3, 29, 32; 1 Cor. 1:9; 15:28; 2 Cor. 1:19; Gal. 1:16; 2:20; 4:4, 6; 1 Thess. 1:10).
9:21-22 Saul's conduct understandably bewildered the Jews who lived in Damascus. Instead of persecuting the Christians he was proving that Jesus was the Christ, the Son of God. This is what people then and now need to believe to obtain salvation. Saul had made a 180 degree change in his thinking and in his conduct; he had truly repented. Saul's understanding and commitment kept growing as he continually sought to convince the Damascus Jews that Jesus was their Messiah. Perhaps Saul's sojourn in Arabia occurred between verses 21 and 22 or between verses 22 and 23.