Paul was fearless because of three experiences he had with Jesus
Experience #1: His Conversion to faith in Jesus: (acts 9:1-20) knowing and remembering how and when you met Jesus is of the utmost importance. What is your conversion story? Where were you? How did God reveal himself to you? Who introduced you to Jesus? Were there any verses that helped you? What did you do in response to Jesus (i.e. pray, get up and go forward) How did you say yes to Jesus free offer of salvation? This will always go with you as you go forward. Remembering how Jesus revealed himself to you will make you grow in fearlessness because you will know the one you serve and his power to reach out to you and transform you.
Experience #2: His time in the wilderness with Jesus. He let Jesus transform his stinking thinking for like several years he listened to only Jesus and no one else that will always grow your fearlessness over a few years (Galatians 1:15-24) Have you let anyone disciple you? If not you should approach someone who you respect spiritually and and ask them to disciple you. Otherwise you may not grow in maturity and will always fear the ways of man. Let someone pour Jesus into you.
Experience #3: His Sufferings for Jesus (Therefore, since Christ has suffered in the flesh, arm yourselves also with the same purpose, because he who has suffered in the flesh has ceased from sin, (1 Peter 4:1 NASB) there is a List of sufferings Paul endured in 2 Corinthians 11:23-33. This had to make him fearless becasue he had to lean on Jesus to even endure these things.
When My youngest brother was in High school he got in a life threatening car accident where he broke his odontoid vertebrae and had bleeding on the brain, and other countless broken bones. My brother faced it with such grace and patience. This kind of suffering can only bring perseverance and grow fearlessness. When we lean on our most fearless leader we too will become fearless. Nick Vujicic is a great story of joy in suffering. His story is a great story of leaning on Jesus, and you tell me what you think. Has he grown to be a fearless person? Enjoy