2 Corinthians 1:14

as also ye have acknowledged us in part that we are your rejoicing, even as ye also are ours in the day of the Lord Jesus.

In expecting that the Corinthians would give thanks on his account as for a gift of grace delivered and restored to them, Paul was placing no small estimate upon his own worth, but he knew that his glorying was of a nature that would not put him to shame. For his act of boasting consisted in this, namely, the witness of his conscience, that in holiness and sincerity of God, not in fleshly wisdom, but in God's grace, he had behaved himself in the world, but more abundantly (than toward anyone else) to the Corinthians. Paul could expect this consideration from the Christians of Achaia, he could be joyfully confident of their prayer and thankfulness, because his moral conduct was above reproach, as his conscience testified to him. The holiness and sincerity which characterized his conduct were divine qualities, they were God's gift to him, of which he made the proper use. And he did not make use of fleshly wisdom, but conducted himself as under the influence of God's grace which had been given to him for the discharge of his apostolic work. Of the faithful Christian conduct of the apostle the Corinthians themselves could testify, for his opportunities at Corinth had been greater than elsewhere for displaying the holiness and sincerity of the Christian life. "Not as though his Christian intercourse with them had been characterized by anything extraordinary, or beyond what he had shown at other places. He intended simply to say: If there are any to whom I have not been manifest as a single hearted and sincere minister of Christ, surely it cannot be you (See 1 Corinthians 9:2), for where in all the world have I been more completely known than among you?"

Paul is absolutely frank with the Corinthians, knowing that his record is above attack: For nothing else do we write to you than what you read or indeed acknowledge. He means what he says, there is no hidden meaning in his letters; and in all his other dealings with them he has not made use of ambiguity; the words of his oral teaching and the communications of his letters agreed exactly. And this state of affairs will continue, his hope being that they will acknowledge him to the end, as also some of you made this acknowledgment. For himself he is asking steadfastness to continue in the pure doctrine and in godly life; for them, that they might acknowledge with a grateful heart what God has given them in the person and through the work of the apostle. For, as Paul says: We are your cause for glorying; the Corinthian Church could well be proud of the fact that he had been their first teacher. And, on the other hand, they represented his reason for glorying on the day of the Lord Jesus Christ. Even before the throne of God he will confess them and boast of them: in their company he wants to appear before the Lord's tribunal and proudly exhibit them as the products of the divine grace.