Matthew Poole and continuators on 2 Corinthians 1:12

12 For our rejoycing is this, the testimony of our consciences, 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-wards .

He declareth the confidence that he had, that he should not want their Prayers, because his own heart told him, to his joy and satisfaction, that however others might reproach him, as if he had carried himself deceitfully, or craftily; yet he had not done so, but had lived in the World in all simplicity and sincerity of God, (so the Greek is.) Simplicity is opposed to double-mindedness; where there is a composition in a man, a mixture of truth and falshood, fairness in speech, and falshood in heart or action. Sincerity is opposed to Hypocrisie. It is said to be of God, because he is the God of Truth, hath commanded it, approveth it, worketh it, and disposeth the heart of man to it.

This is opposed to fleshly Wisdom, which prompteth a man to seek his own ends any way, good or bad.

But (saith the Apostle) we have had our conversation in the World, not by the guidance of any such corrupt habit or Principle, but by the Grace of God, the love and fear of God dwelling in us; or, we have done this, not of our selves, but, by the guidance and assistance of Divine Grace, helping us so, to live, and to have our conversation in the World.

And more especially you are our Witnesses of this, amongst whom we have preached the Gospel freely, so as we have not made it chargeable to you.