This is the only time that the phrase Son of God
will be used in Acts, though it is found often in Saul’s letters (Romans 1:1–4; 1 Thessalonians 1:10; Galatians 2:20; Ephesians 4:13).1 Son of God is a phrase that expresses the unique standing of Jesus and the intimate favour he enjoys with God.2,3 For Saul, it denotes Jesus’ ontological equality with God the Father and his glorious exaltation as the representative and mediator of God’s people.4 In the Old Testament is refers to the Messiah (2 Samuel 7:14) who will be exalted by God to sit at his right hand (Psalm 2:7).5
20 And immediately he proclaimed Jesus in the synagogues, saying, “He is the Son of God.”