What does 2 Corinthians 9:15 mean?

This wraps up Paul's appeal to the Corinthians to participate willingly and cheerfully in giving generously to meet the needs of the suffering Jerusalem Christians. His concluding declaration is, "Thanks be to God for his inexpressible gift!" In the end, Paul's focus is not on the gift of money he wants the Corinthians to collect for the Jerusalem believers, it is on God's gift to all who are in Christ.

Paul describes God's gift as "inexpressible," but he may be referring to several different things. Perhaps he has in mind what he wrote about Christ's sacrificial gift to humanity in the previous chapter, "For you know the grace of our Lord Jesus Christ, that though he was rich, yet for your sake he became poor, so that you by his poverty might become rich" (2 Corinthians 8:9).

Or, Paul may be calling attention to an idea about the opportunity to participate in increasing righteousness and thankfulness to God on earth. These "harvests" are a gift to those who give generously. The opportunity to give and the cascade of good things that come from giving generously, in the end, provide great meaning and satisfaction to those who give in submission to Christ.