He Declares That He Has Been Faithful To Them And To All (2 Corinthians 1:12-14)
‘For our glorying is this, the testimony of our conscience, that in holiness and sincerity of God, not in fleshly wisdom but in the grace of God, we behaved ourselves in the world, and more abundantly to you-ward.'
Having established the fact of God's great saving activity, and in return for their faithful prayers (2 Corinthians 1:11), he now wants them to be confident about the concern that he has for them. From a true conscience he ‘glories' in how he has behaved towards the world, and especially ‘more abundantly' towards them, in holiness and sincerity/purity of motive, a sincerity/purity of motive which he has put to the test before God and about which he has received clearance (‘of God'). And also in the grace of God rather than in fleshly wisdom. He is already indirectly rebutting the charge of fickleness found in 2 Corinthians 1:17, of ulterior motives (see 2 Corinthians 2:17; 2 Corinthians 4:2) and of dishonesty (2 Corinthians 8:20; 2 Corinthians 12:14).
He wants them to know that he has carefully examined his conscience, and that it is absolutely clear. He has no doubts that the grace of God is at work through him, so that he acts through God's wisdom and not his own, and that what he is doing is being done in holiness and sincerity, as one totally set apart to God and one who is genuine through and through. (Let them recognise this and ask if the same is true of his opponents). Would that we all did the same.
Note the contrast between ‘fleshly-wisdom' and ‘divine-grace' (grace of God). Paul is borne along, not by some doubtful ‘wisdom' which is really of the flesh (a hit at his opponents, compare 1 Corinthians 1:17; 1 Corinthians 2:4; 1 Corinthians 2:13), but by the unmerited favour and activity of the living God, which is ‘of God'.