Why did God raise up Saul of Tarsus as an apostle?
God raised up Saul of Tarsus as an apostle because Israel rejected and crucified the Messiah and continued rejecting Him, proving they would not believe. Saul, a rebel who hated Jesus, was saved by grace and sent far hence to the Gentiles, while Israel entered spiritual blindness, opening the Gospel to pagan Gentiles.
Les explains that Israel could have had the King and the Kingdom and could have evangelized the Gentiles, but in God's foreknowledge that could not happen; the Messiah had to die. Israel rejected and crucified Him and continued rejecting Him in the early Acts, though Peter and the eleven preached. When Israel proved they would not believe, God raised up Saul, that rebel and raging bull who hated Jesus of Nazareth, and saved him by grace—the epitome of grace. God told Saul before he got out of Damascus that He would send him far hence to the Gentiles. Israel would go into spiritual blindness, but Saul would go to the Gentiles. Israel's rejection opened the windows of heaven for pagan Gentiles, who swarmed to the Gospel with spiritual hunger.