A.T. Robertson Commentary 2 Corinthians 13:9

"For we rejoice, when we are weak, and ye are strong: this we also pray for, even your perfecting." — 2 Corinthians 13:9 (ASV)

For we rejoice (χαιρομεν γαρ). Paul had far rather be weak in the sense of failing to exercise his apostolic power because they did the noble thing. He is no Jonah who lamented when Ninevah repented.

Your perfecting (υμων καταρτισιν). Late word from καταρτιζω, to fit, to equip (see verb in verse 11). In Plutarch, only here in N.T.