A.T. Robertson Commentary 1 Corinthians 9:23

"And I do all things for the gospel`s sake, that I may be a joint partaker thereof." — 1 Corinthians 9:23 (ASV)

That I may be a joint partaker thereof (ινα συνκοινωνος αυτου γενωμα). Literally, That I may become co-partner with others in the gospel. The point is that he may be able to share the gospel with others, his evangelistic passion. Συνκοινωνος is a compound word (συν, together with, κοινωνος, partner or sharer). We have two genitives with it in Php 1:7, though εν and the locative is used in Re 1:9. It is found only in the N.T. and a late papyrus. Paul does not wish to enjoy the gospel just by himself.