God sets apostles and prophets in the church. Prior to the call to ministry, God established a divine connection between Saul and Barnabas for kingdom purposes. Then the Holy Spirit set them apart for a special work together. Immediately afterwards, the proconsul called them to minister the Word of God to him. You must know to whom you are assigned as well as the gift(s) for the ministry. God already has people on the other side waiting to be serviced by you. Obey and trust God.