1 Corinthians 9:17-19 New International Version - UK (NIVUK)
17 If I preach voluntarily, I have a reward; if not voluntarily, I am simply discharging the trust committed to me. 18 What then is my reward? Just this: that in preaching the gospel I may offer it free of charge, and so not make full use of my rights as a preacher of the gospel.
Paul’s use of his freedom
19 Though I am free and belong to no one, I have made myself a slave to everyone, to win as many as possible.