“Having therefore obtained the help that is from God, I stand, to this day, testifying both to small and great, saying nothing but what the prophets and Moses did say should come, how that the Christ must suffer, and how that he first by the resurrection of the dead should proclaim light both to the people and to the Gentiles.”
And central to all this is Jesus the Christ and the resurrection (compare Acts 17:18). That is why he has received help from God. It was in order that he might proclaim to both small and great the hope of Israel as revealed by Moses and the prophets, namely that the Messiah must come, and that He must suffer, and that through His resurrection He would proclaim light to both Jews and Gentiles. For it is finally His resurrection that is the proof of what God has done and which therefore brings light to all (compare 1 Corinthians 15:14; 2 Timothy 1:10).
And he wants them to recognise that in teaching these things he is saying nothing other than the prophets have already said. Scriptures he has in mind would included Deuteronomy 18:18, of the coming Prophet; Isaiah 53:10-12 which could only be fulfilled by the resurrection of the Servant; Isaiah 52:13, where the One Who had been humiliated is exalted high; both halves of Psalms 22, expressing humiliation and triumph; the triumph of the Messiah in Psalms 16:8-11; Psalms 110:1; Moses teaching on the sacrifices which are fulfilled in Christ (1 Corinthians 5:7) and are for the forgiveness of sins; Isaiah 42:6; Isaiah 49:6 where the Servant is shown to be for the light to the Gentiles.