As they ministered to the Lord and fasted, the Holy Spirit said, "Now separate to Me Barnabas and Saul for the work to which I have called them." Then, having fasted and prayed, and laid hands on them, they sent them away. – Acts 13.2-3
Saul and Barnabas returned from a trip to Jerusalem. The brought John Mark with them and came back to the church in Antioch.
Gods work was expanding. The church was Anticoh was growing. They had a group of preachers there: Barnabas, Simon, Lucius, Manaen (who by the way, had been raised with Herod, and Saul. As these men served and ministered and prayed the Holy Spirit directed the church to 'separate Saul and Barnabas to she work God called them to do. God's work was for them to go preach the gospel and start churches.
This is just, the start of their great missionary partnership. Even though I believe God has called us and put us where we are I don't fully understand how this 'call' works, but I do know that God still calls and still directs local churches to separate their people to ministry outside their church.
God set a pattern for service early on. God calls people to do His, the church rallies behind them, fasts and prays, and sends them out. Its really pretty simple. Its too bad we tend to complicate it so much.
Praise God for His diving plan to send His servants.