Rev., correctly, He hath said. The force of the perfect tense is to be insisted on. It shows that the affliction was still clinging to Paul, and that there was lying in his mind when he wrote, not only the memory of the incident, but the sense of the still abiding power and value of Christ's grace; so that because the Lord hath said “my grace,” etc., Paul can now say, under the continued affliction, wherefore I take pleasure, etc., for Christ's sake; for when I am weak, then am I strong. A more beautiful use of the perfect it would be difficult to find in the New Testament.
The best texts omit my, thus turning the answer into a general proposition: strength is perfected in weakness; but besides the preeminent frigidity of replying to a passionate appeal with an aphorism, the reference to the special power of Christ is clear from the words power of Christ, which almost immediately follow. Compare 1Co 2:3, 1Co 2:4; 2Co 4:7; Heb 11:34. Rev., rightly, retains my italicized.
May rest upon (ἐπισκηνώσῃ)
Only here in the New Testament. The simple verb σκηνόω to dwell in a tent is used by John, especially in Revelation. See on Joh 1:14. The compound verb here means to fix a tent or a habitation upon; and the figure is that of Christ abiding upon him as a tent spread over him, during his temporary stay on earth.
For Christ's sake
This may be taken with all the preceding details, weaknesses, etc., endured for Christ's sake, or with I take pleasure, assigning the specific motive of his rejoicing: I take pleasure for Christ's sake.