While they were worshiping the Lord and fasting, the Holy Spirit said, “Set apart for me Barnabas and Saul for the work to which I have called them.” Then after fasting and praying they laid their hands on them and sent them off.
(Acts 13:2-3 ESV)
For the work to which I have called them…. God had a specific work for Barnabas and He had a specific work for Saul(Paul) to do. Paul would later write in Ephesians 2:10:
For we are His workmanship, created in Christ Jesus for good works, which God prepared beforehand that we should walk in them.
God was calling Barnabas and Saul to these good works now!
God had already started this calling He had for the life of Paul. Acts 9:15-16:
He is a chosen vessel of Mine to bear My name before Gentiles, kings, and the children of Israel. For I will show him how many things he must suffer for My name’s sake.
This was not a sentimental, “feel good” call – it was a serious call to a serious ministry. It was a call to share the Good News of Jesus, even when it meant sure suffering.