|Lake Michigan, from Warren Dunes State Park|
In Acts 13:2-3 we read:
Now there were in the church at Antioch prophets and teachers, Barnabas, Simeon who was called Niger, Lucius of Cyrene, Manaen a lifelong friend of Herod the tetrarch, and Saul. 2 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.” 3 Then after fasting and praying they laid their hands on them and sent them off.
Here we have an important moment in the life of the early church (the early Jesus-community). Paul has already been chosen to carry the name of Jesus before "Gentiles and kings and the children of Israel." (Acts 9:15-16) This prophetic word had not yet come to pass. "What it suggested was that Paul would at some point become the central human character in the narrative." (Witherington, The Acts of the Apostles, 391)
From this point on in Acts 13, this prophetic calling on Paul comes to pass.
In verse 2 we see the disciples of Jesus worshiping. Their act of worship included fasting. Why? Witherington writes: "It is not possible to determine from this elliptical remark whether the leaders sere simply given to fervency in their devotions or were seeking some specific guidance on a matter through intense worship and fasting." (Ib., 393)
In the midst of their worship and fasting the Holy Spirit called to them: “Set apart for me Barnabas and Saul for the work to which I have called them.” Scot McKnight says the emphasis of this passage (and others like it) is "the yearning of God's people to know his will." (McKnight, Fasting, 49) God revealed his will. It was time for the prophetic word given earler to Paul to be fulfilled.
Note that the disciples did not first take some action and then pray and fast about it afterwards. Rather, they first prayed and fasted, and in the midst of their worship God revealed more details of his will. So one of the things you and I can expect while prayer-fasting is a greater revelation of the will of God for us and our Jesus-community.