The Spirit spoke through the leaders at the church in Antioch and directed them to set apart Saul and Barnabas for the work to which God had called them. Acts 13:4-12 clarifies what that work is:

13:4 So Barnabas and Saul, sent out by the Holy Spirit, went down to Seleucia, and from there they sailed to Cyprus. 13:5 When they arrived in Salamis, they began to proclaim the word of God in the Jewish synagogues. (Now they also had John as their assistant.) 13:6 When they had crossed over the whole island as far as Paphos, they found a magician, a Jewish false prophet named Bar-Jesus, 13:7 who was with the proconsul Sergius Paulus, an intelligent man. The proconsul summoned Barnabas and Saul and wanted to hear the word of God. 13:8 But the magician Elymas (for that is the way his name is translated) opposed them, trying to turn the proconsul away from the faith.13:9 But Saul (also known as Paul), filled with the Holy Spirit, stared straight at him 13:10 and said, “You who are full of all deceit and all wrongdoing, you son of the devil, you enemy of all righteousness – will you not stop making crooked the straight paths of the Lord? 13:11 Now look, the hand of the Lord is against you, and you will be blind, unable to see the sun for a time!” Immediately mistiness and darkness came over him, and he went around seeking people to lead him by the hand. 13:12 Then when the proconsul saw what had happened, he believed, because he was greatly astounded at the teaching about the Lord.

They are to proclaim the word of God in Jewish synagogues, and they do this on the island of Cyprus — across the whole. In this process of preaching the word in synagogues and gospeling, they encounter a magician, a Jewish false-prophet named Bar-Jesus (son of Yeshua). Again, we are using Beverly Gaventa’s The Acts of the Apostles (Abingdon New Testament Commentaries)
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But Saul (also known as Paul), filled with the Holy Spirit, stared straight at him 13:10 and said, “You who are full of all deceit and all wrongdoing, you son of the devil, you enemy of all righteousness – will you not stop making crooked the straight paths of the Lord? 13:11 Now look, the hand of the Lord is against you, and you will be blind, unable to see the sun for a time!” Immediately mistiness and darkness came over him, and he went around seeking people to lead him by the hand. 13:12 Then when the proconsul saw what had happened, he believed, because he was greatly astounded at the teaching about the Lord.