Now this is our boast: Our conscience testifies that we have conducted ourselves in the world, and especially in our relations with you, with integrity and godly sincerity. We have done so, relying not on worldly wisdom but on God's grace.
NIV
It is a reason for pride and exultation to which our conscience testifies that we have conducted ourselves in the world [generally] and especially toward you, with devout and pure motives and godly sincerity, not in fleshly wisdom but by the grace of God (the unmerited favor and merciful kindness by which God, exerting His holy influence upon souls, turns them to Christ, and keeps, strengthens, and increases them in Christian virtues).
AMP
For our rejoicing is this, the testimony of our conscience, that in simplicity and godly sincerity, not with fleshly wisdom, but by the grace of God, we have had our conversation in the world, and more abundantly to you-ward.
KJV