2 Corinthians 7:13-16 (Holman Christian Standard Bible)
13 For this reason we have been comforted.
In addition to our comfort, we were made to rejoice even more over the joy Titus had, because his spirit was refreshed by all of you. 14 For if I have made any boast to him about you, I have not been embarrassed; but as I have spoken everything to you in truth, so our boasting to Titus has also turned out to be the truth. 15 And his affection toward you is even greater as he remembers the obedience of all of you, and how you received him with fear and trembling. 16 I rejoice that I have complete confidence in you.
Paul had sent a second letter to Corinth by Titus. That second letter was a harsh letter, meant to chastise the Corinthians and encourage them to Godly obedience. It was a harsh letter which would not have been easy to read because it told the truth. He had sent the letter to them instead of visiting them because of the message of the letter, Paul thought that it would be better for them to read all of what he had to say instead of hearing it and remembering only the parts they chose to remember.
Instead of going to Corinth, Paul went to Troas to preach the gospel but his concern for the Corinthians was such that he could not preach. He had hoped to meet Titus there with news of the reception of the letter, but when Titus did not show Paul could not preach. So he went on ahead to Macedonia where finally Titus came with news from Corinth.
Paul describes the discouragement he was feeling as he waited for Titus. He felt falsely accused in actions, teachings and motives. He went without rest, being harassed everywhere he went and enduring conflicts which produced fears within. He had experienced all of these things before, but with the added worry of the Corinthians these things began to weigh heavily on him. He was depressed. He felt alone. He was losing sight of hope and beginning to doubt his ministry.
With joy Paul expresses the comfort that came to him when Titus shared the good news about the response of the Corinthians to his letter.