1 Corinthians 9:16-23 NRSV
If I proclaim the gospel, this gives me no ground for boasting, for an obligation is laid on me, and woe to me if I do not proclaim the gospel! For if I do this of my own will, I have a reward; but if not of my own will, I am entrusted with a commission. What then is my reward? Just this: that in my proclamation I may make the gospel free of charge, so as not to make full use of my rights in the gospel.
For though I am free with respect to all, I have made myself a slave to all, so that I might win more of them. 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 I myself am not under the law) so that I might win those under the law. To those outside the law I became as one outside the law (though I am not free from God's law but am under Christ's law) so that I might win those outside the law. To the weak I became weak, so that I might win the weak. I have become all things to all people, that I might by all means save some. I do it all for the sake of the gospel, so that I may share in its blessings.
NRSV: New Revised Standard Version