1 Corinthians 9:18
What is my reward then? Verily that, when I preach the gospel, I may make the gospel of Christ without charge, that I abuse not my power in the gospel. What is my reward then? Verily that, when I preach the gospel, I may make the gospel of Christ without charge, that I abuse not my power in the gospel.
Paul had the right to receive support from those he served, but he gave up that right in order to preach the gospel without charge. Instead of living on the support to which he was entitled, he supported himself by laboring with his own hands. By so doing he showed that he was working for the salvation of souls and not for money. By so doing he also avoided abusing and misusing his authority and power as a minister of the gospel.
He surrendered his right at Corinth so that no one there could suspect or accuse him of preaching to enrich himself or for money. He did this to protect his usefulness and to keep suspicion of financial gain from weakening the force of his message. Such precaution was needed in Corinth, where people treated gain as godliness and were suspicious of the motives of strangers.