1 Corinthians 9:13-27 (ESV)
13 Do you not know that those who are employed in the temple service get their food from the temple, and those who serve at the altar share in the sacrificial offerings? 14 In the same way, the Lord commanded that those who proclaim the gospel should get their living by the gospel.
15 But I have made no use of any of these rights, nor am I writing these things to secure any such provision. For I would rather die than have anyone deprive me of my ground for boasting. 16 For if I preach the gospel, that gives me no ground for boasting. For necessity is laid upon me. Woe to me if I do not preach the gospel! 17 For if I do this of my own will, I have a reward, but if not of my own will, I am still entrusted with a stewardship. 18 What then is my reward? That in my preaching I may present the gospel free of charge, so as not to make full use of my right in the gospel.
19 For though I am free from all, I have made myself a servant to all, that I might win more of them. 20 To the Jews I became as a Jew, in order to win Jews. To those under the law I became as one under the law (though not being myself under the law) that I might win those under the law. 21 To those outside the law I became as one outside the law (not being outside the law of God but under the law of Christ) that I might win those outside the law. 22 To the weak I became weak, that I might win the weak. I have become all things to all people, that by all means I might save some. 23 I do it all for the sake of the gospel, that I may share with them in its blessings.
24 Do you not know that in a race all the runners run, but only one receives the prize? So run that you may obtain it. 25 Every athlete exercises self-control in all things. They do it to receive a perishable wreath, but we an imperishable. 26 So I do not run aimlessly; I do not box as one beating the air. 27 But I discipline my body and keep it under control,  lest after preaching to others I myself should be disqualified.