Acts 10 records the story of a man named Cornelius, a centurion who lived in Caesarea. Caesarea was a Roman outpost in Israel, named after Caesar. As a Roman military officer who commanded a group of 100 soldiers, Cornelius would have been taught to worship the gods of Rome that mostly were from Greece, which Rome conquered. He also would have been taught to worship Caesar as a god. Yet this worship apparently left Cornelius feeling empty.
Being around the Jewish people all the time, maybe he thought, You know, I believe they are worshiping the true God.
So he started giving money to the poor, and he started praying to the God of Israel. Even though he was a non-Jew, he called out to their God. God will reveal Himself to the true seeker (see Jeremiah 29:13), and because Cornelius was truly seeking God, He sent an angel to tell him to summon Peter, who would have a message for him.
But the angel didn't cut to the chase and say, "Hey, Cornelius! You need to believe in Jesus, who died and rose again." Why not give him the gospel right then and there? Because the primary way that God reaches people is through people. Romans 10:14 says, "But how can they call on him to save them unless they believe in him? And how can they believe in him if they have never heard about him? And how can they hear about him unless someone tells them?"
Peter was the man whom God wanted to use to reach Cornelius. God wanted Cornelius to be saved, and He also wanted to use the conversion of Cornelius, a Gentile, to open Peter's eyes to the fact that there is a big world out there that needs to hear the gospel.