What was the purpose of fasting in Acts 13:1-3?

Acts 13:1-3 (ESV):

1 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.

What were they fasting for? How did the fasting help?

Related: What’s the purpose of fasting and prayer in Acts 14:23?