12 For our boasting is this: the testimony of our conscience that we conducted ourselves in the world in simplicity and godly sincerity, not with fleshly wisdom but by the grace of God, and more abundantly toward you.
13 For we are not writing any other things to you than what you read or understand. Now I trust you will understand, even to the end
14 (as also you have understood us in part), that we are your boast as you also are ours, in the day of the Lord Jesus.
boasting (v.12) = glorying, exultation
testimony (v.12) = witness, evidence, proof
Paul’s action with [the members of the Corinthian church] were sincere, disinterested, and affectionate (v.12). He wrote nothing to them but what they had already received and read and acknowledged to be true (v.13); but only a “part” of them acknowledged and recognized his sincerity (v.14). These rejoiced in Paul as he looked forward to rejoicing in them at the coming of the Lord. — Williams, page 897
For our glorying is this, the testimony of our conscience, that in the holiness, purity and unsullied character of God, not in human wisdom, but by God’s grace we ordered our behavior in the world, and this was more abundantly evident to you. For, no other things are we writing to you but those things which you are reading or even acknowledge to be what they really are, and which I hope you will acknowledge to the end, as also certain ones of you acknowledged us for what we really are, that we are even as that in which you glory, and you are that in which we glory in the day of our Lord Jesus. — Wuest, page 418
Paul has much to say about conscience, and how earnestly he strove always to have a clear conscience. What power this lent to his ministry for Christ! He could look the unscrupulous members of the Sanhedrin sternly in the eye, and say to them: “Men and brethren, I have lived in all good conscience before God until this day” (Acts 23:1).
Little wonder this so offended the high priest, whose conscience had already been “seared with a hot iron,” that he commanded those who stood by to smite Paul on the mouth (Acts 23:2). — Stam, page 41.
The marks of Paul’s good conscience and thus of his spiritual integrity, were his “simplicity and Godly sincerity.” Though he was endowed with a keen intellect, yet his preaching was “not with fleshly wisdom” but “by the grace of God.” This was how he conducted himself not only “in the world,” but “more abundantly” toward them. Thus simply, by “manifestation of the truth” he commended [himself] to every man’s conscience in the sight of God” (2 Corinthians 4:2). — Stam, page 41.
The Greek word for “sincerity” in 2 Corinthians 1:12 is a long one: eilikrineis, meaning literally, to judge of in the sunlight, and it is interesting to learn how this phrase-in-a-word became one of the four Greek terms used for sincerity.
The Greeks produced many beautiful urns, vases, bowls and pitchers with colored designs, glistening from the coats of lacquer that covered them. Many of these are still in existence today.
Sometimes, however, the lacquer, or even the vessel itself, would develop a crack, which some dealers in these items would fill with colored wax to match the surrounding color. The defect would thus become virtually invisible—unless the vessel was held up to the sunlight! — Stam, page 41.
In verse 13 the apostle refers, evidently, to his first letter to them, declaring “We write none other things unto you than what ye read or acknowledge.” They had read what he had written and that was exactly what he had meant. There was no “craftiness” in his writings, no hidden meanings. The letter had indeed been one of rebuke and warning, but it had been written “out of much affliction and anguish of heart” and “with many tears” and an abundance of love (2 Corinthians 2:4). Some of its truths, he says, they had already acknowledged and, he hoped, would continue to acknowledge “to the end.” — Stam, page 42.
But even though acknowledged only “in part,” [Paul] says of that “part”: “… we are your rejoicing, even as ye are ours in the day of the Lord Jesus.” This reminds us of what he had previously written to his beloved Thessalonian friends, those faithful partners in persecution: “What is our hope, or joy, or crown of rejoicing? Are not even ye in the presence of our Lord Jesus Christ at His coming?” (1 Thessalonians 2:19).
If he was their “rejoicing,” they were certainly his. It was his deep and constant joy that when finally called to be with Christ at the Rapture, they would be there too as demonstrations of the riches of God’s grace. — Stam, page 43.