Why did Barnabas bring Saul to Antioch?

Barnabas brought Saul to Antioch because God had revealed Saul was the man needed to carry the message to the Gentiles. God had opened Gentile hearts and was opening the door for the gospel to move into the Gentile world, so Saul was needed to teach the Antioch believers for a whole year.

Les explains that Barnabas told Saul things were happening at Antioch and that God had revealed to him Saul was the man they had to have. Saul was the one with the message now for the Gentiles. God had opened their hearts and was opening the door, moving into the Gentile world. So Barnabas brought Saul to Antioch, and for a whole year they assembled with the church and taught many people. There the disciples were first called Christians, because Antioch was being presented with Paul's Gospel—the secret held in God's mind until revealed—distinguishing it from the earlier Jewish believers who only believed Jesus was Messiah.

What did Barnabas and Saul do during their first year in Antioch?

During their first year in Antioch, Barnabas and Saul assembled together with the church and taught much people. The disciples there, primarily Gentiles, were first called Christians in Antioch, because Antioch was being presented with Paul's Gospel, differentiating it from the Judaistic believers in Jerusalem.