2 Corinthians 13:9 For we are glad, when we are weak, and ye are strong: and this also we wish, even your perfection.

The Apostle Paul’s desire was for the Corinthian church to move toward spiritual maturity, to be spiritually equipped and strong. He sought that the sinning ones in their midst will come back to God, repent of their sins and be restored in fellowship with God’s people. Hodge said well, “Paul prayed that they might be perfectly restored from the state of confusion, contention and evil into which they had fallen.”

As to why they were glad when they were weak? Gill observed well, “Appear to be so, look like persons disarmed of all power and authority; the apostles rejoiced when they had no occasion of exerting themselves, and of exercising that high office, and extraordinary commission they had received of Christ Jesus.”