What does Paul mean by 'your rejoicing' in 1 Corinthians 15:31?
Paul means the Corinthians’ rejoicing in Christ Jesus, which he also shares in the Lord. Even though they were carnal Christians, they still had reason to rejoice in Christ. He affirms by that shared rejoicing that he dies daily, making their joy the ground of his solemn assertion.
Les explains that in 1 Corinthians 15:31 the King James word is 'protest,' but a later Greek text uses 'affirm,' which makes better sense. Paul writes to a carnal congregation, not spiritual, yet he is giving deep doctrinal teaching on resurrection. He reminds them that he affirms by their rejoicing—their joy in Christ Jesus, which he also has in the Lord. Even as carnal Christians, they had enough sense to rejoice in certain things. Paul then says, 'and by that I have in Christ Jesus our Lord, I die daily.' Les notes a two-fold approach to 'I die daily,' beginning with the old and new nature.
I protest by your rejoicing which I have in Christ Jesus our LORD, I die daily.