1 Corinthians 9:16-17

Telling the Good News does not give me any reason for bragging. Telling the Good News is my duty—something I must do. And how terrible it will be for me if I do not tell the Good News. If I preach because it is my own choice, I have a reward. But if I preach and it is not my choice to do so, I am only doing the duty that was given to me.