What does “When that which is perfect is come;”(1 Cor. 13:9) mean?

I think you are asking about 1 Corinthians 13:9-10, “ For we know in part, and we prophesy in part; but when the perfect comes, the partial will be done away.” This is a somewhat debated passage, but I will share a couple of the prominent viewpoints on this passage. I also suggest you read Greg Herrick’s article, The Argument of 1 Corinthians 12-14 on our web site.

13:9-10. As Paul explained it, the gift of knowledge (v. 8), essential as it was, was not exhaustive. The ability to prophesy, however crucial for the church’s life, was of limited scope. The gifts were temporary blessings in an imperfect age. One day they would give way to perfection, toward which all the gifts pointed.

What Paul meant when he referred to the coming of perfection is the subject of considerable debate. One suggestion is that perfection described the completion of the New Testament. But verse 12 makes that interpretation unlikely. A few have suggested that this state of perfection will not be reached until the new heavens and new earth are established. Another point of view understands perfection to describe the state of the church when God’s program for it is consummated at the coming of Christ. There is much to commend this view, including the natural accord it enjoys with the illustration of growth and maturity which Paul used in the following verses. [Walvoord, John F., and Zuck, Roy B., The Bible Knowledge Commentary, (Wheaton, Illinois: Scripture Press Publications, Inc.) 1983, 1985.]