If he would believe it means God God caused him to by His Spirit, and it meant he had been ordained to eternal life, chosen Acts 13:48
48 And when the Gentiles heard this, they were glad, and glorified the word of the Lord: and as many as were ordained to eternal life believed
This message made the Gentiles glad, and they praised what they had heard about the Lord. Everyone who had been chosen for eternal life then put their faith in the Lord. CEV
For someone that claims to have studied the bible for 50 yrs, you do seem to have problems understanding context.
Act 13:46 Then Paul and Barnabas answered them boldly: “It was necessary to speak the word of God to you first. But
since you reject it and do not consider yourselves worthy of eternal life, we now turn to the Gentiles.
Act 13:47 For this is what the Lord has commanded us: ‘I have made you a light for the Gentiles, to bring salvation to the ends of the earth.’”
Act 13:48
When the Gentiles heard this, they rejoiced and glorified the word of the Lord, and all who were appointed for eternal life believed.
The gentiles had heard Paul's gospel message, those that accepted it and trusted in the one spoken of took that direction for eternal life, and believed. Act_13:26-52 is showing the contrast between the resistant Jews and the willing Gentiles and should be read in a way that places the responsibility for believing on the people, that the people positioned themselves either for eternal life by accepting the truth or for eternal death by rejecting it.