1 Corinthians 9:18 Meaning

16For though I preach the gospel, I have nothing to glory of: for necessity is laid upon me; yea, woe is unto me, if I preach not the gospel!

17For if I do this thing willingly, I have a reward: but if against my will, a dispensation of the gospel is committed unto me.

18What 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.

19For though I be free from all men, yet have I made myself servant unto all, that I might gain the more.

20And unto the Jews I became as a Jew, that I might gain the Jews; to them that are under the law, as under the law, that I might gain them that are under the law;