What does 1 Corinthians 9:18 mean?
Paul does not take any credit for the content of the gospel message about salvation through faith in Christ by God's grace. That all comes from God. He also does not take credit for the outcome of his preaching. More than that, he has stated flatly that he does not even take credit for his participation in preaching the gospel. He simply has no choice. He is compelled by Christ, as a trusted servant, to carry out this task. He receives no reward for it, as if it was his idea or something he did out of the nobility of his own heart.Now he adds that he does receive a reward, in a sense. In refusing to exercise his right to receive financial support from those he serves, Paul can claim a degree of self-sacrifice. He gets to boast a bit: that he is legitimately giving up something for the Lord. This is not an arrogant, self-serving boast. It is a joyful claim that he is sacrificing something he is not required to give. God does not command Paul to turn down donations for his ministry; prior verses showed that God expects those served by ministers of the gospel to support those ministers (1 Corinthians 9:9, 14). Paul does so willingly and receives the reward of knowing that he is doing so.
He receives the award of gratification in giving away the good news about Jesus for free. In part, his reward includes the right to boast—righteously, in joy, not in arrogance—about this selfless action.