Albert Barnes on 2 Corinthians 12:19

Again, think ye that we excuse ourselves unto you? 2Cor 5:12. The sense is, do not suppose that this is said from mere anxiety to obtain your favour, or to ingratiate ourselves into your esteem. This is said doubtless to keep himself from the suspicion of being actuated by improper motives, he had manifested great solicitude certainly in the previous chapters to vindicate his character; but he here says that it was not from a mere desire to show them that his conduct was right; it was from a desire to honour Christ.

We speak before God in Christ. We declare the simple and undisguised truth as in the presence of God. I have no mere desire to palliate my conduct; I disguise nothing; I conceal nothing; I say nothing for the mere purpose of self-vindication; but I can appeal to the Searcher of hearts for the exact truth of all that I say. The phrase "before God in Christ" means, probably, "I speak as in the presence of God and as a follower of Christ, as a Christian man." It is the solemn appeal of a Christian to his God for the truth of what he said, and a solemn asseveration that what he said was not for the mere purpose of excusing or apologizing for (Greek) his conduct.

But we do all things, dearly beloved, for your edifying. All that I have done has been for your welfare. My vindication of my character, and my effort to disabuse you of your prejudices, have been that you might have unwavering confidence in the gospel, and might be built up in holy faith. On the word edify, Rom 14:19, 1Cor 8:1; 1Cor 10:23.

(*) "excuse" "defend" (c) "ourselves" 2Cor 5:12