What does Acts 13:21 mean?

Barnabas and Paul are in Pisidian Antioch, near the center of modern-day Asia Minor, during their first missionary voyage. Paul is giving the message in a synagogue to an audience of Jews and God-fearing Gentiles. He is introducing the spiritual salvation Jesus offers by replaying God's saving work in the history of Israel.

King Saul is an interesting individual for Paul to use. He was not God's choice for a king; the people demanded a king and God allowed them to have the type of king they thought they wanted. Saul's fear, jealousy, and disrespect of God led to Israel's defeat in battle and the deaths of himself and his sons (1 Samuel 31).

But Saul did take an assortment of religiously and historically related tribes and turn them into a coherent political nation. And God did save Israel from several enemies during Saul's reign, even if many of those battles were won by Saul's son Jonathan or by David.

Paul did not need to elaborate on King Saul's flaws. Paul's hearers would know the history of Israel well, and Paul is likely anxious to get to his next point. Paul is trying to communicate to his audience that God's plan all along was to bring salvation not through the people-endorsed Saul but through David, the man after His own heart. It is also interesting to note that Paul's Jewish name is Saul and he, too, is of the tribe of Benjamin (Philippians 3:5). Where the Old Testament Saul rejected God and was lost, Paul submitted to Christ and was saved.

It is through David that God intended to establish the kingly line of Israel, culminating in the Messiah—the ultimate Savior. Paul's audience will have to make a choice. Will they put their faith in what looks good—the Law and human effort—like their ancestors did when they took Saul as king? Or will they wait on the Lord, accept that His plan always involved the Messiah born in David's line, and accept Jesus?