For 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!
Though I (if I simply) preach ... I have nothing to glory of - for the "necessity" laid on me by Christ's commission (Acts 26:16-18) to preach (cf. Jeremiah 20:9, and Jonah) does away with "glorying." It is only when I preach without charge (1 Corinthians 9:18) that I have cause for "glorying," since there is no necessity laid on me as to this: it is my voluntary act for the Gospel's sake.