How did Barnabas know Saul should take the message to the Gentiles?
God revealed to Barnabas that Saul was the man they needed and the one who had the message for the Gentiles. Barnabas also recognized that God had opened the Gentiles' hearts and was opening the door, showing that God was going to move out into the Gentile world.
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—the one with the message for the Gentiles. Barnabas saw that God had opened the Gentiles' hearts and was opening the door, evidently moving into the Gentile world. He then brought Saul to Antioch, where for a whole year they assembled with the church and taught many people. It was there the disciples were first called Christians. Les contrasts this with Jerusalem, which had held forth for twelve years but never called its Jewish believers Christians; they remained under the Judaistic umbrella, believing only that Jesus was Israel's Messiah. The Antioch believers, however, believed He had died for them, shed His blood for their sin, and was raised from the dead. Antioch was now being presented with Paul's Gospel, which differed from everything before—a secret held in God's mind until revealed, showing God was doing something totally different.