In this portion of Paul's instructions to the Corinthians about giving, Paul emphasizes the importance of accountability—not only before God, but also in the eyes of men. The significance of integrity in the financial dealings of the church can be highlighted by looking at the different personalities Paul mentions in this passage.
I. TITUS' EARNEST CARE (vv. 16-17).
A. Titus was the one who, originally, inspired this effort of giving on the part of the Corinthians (v. 6). Now; Paul expresses gratefulness to God that this same earnest care that Paul described in verses 10-15 is also in Titus. Note that, when someone is moved to do good in the name of Jesus, it's ultimately to God that the thanks belong (v. 16).
B. Titus not only accepted the exhortation of Paul (v. 6), but he willingly went of his own accord. Paul didn't really need to urge him to do so; because he wanted to do so. Paul puts emphasis on Titus' "earnestness". It's this sort of earnestness that seeks to protect the integrity of the people of God in the matter of giving (v. 17).
II. THE PRAISE-WORTHY BROTHER SENT BY THE CHURCHES (vv. 18-21).
A. It's not enough that Titus go alone. With him, Paul also sent an unnamed "brother". It may be that Paul had practical reasons for avoiding the mention of this man's name in the letter. But whoever he is, he is someone who had a good reputation. His praise is "in the gospel throughout all the churches" (v. 18). He's someone who has earned a good and faithful reputation in the body of Christ, both with respect to his work in the spread of the gospel and in his standing in it.
B. Not only does Paul endorse him by his good reputation in the gospel, but he also affirms that he was chosen for this particular work toward the Corinthians by the churches at large (v. 19). When examining someone's credentials with respect to the business matters of the church, we should consider carefully the standing he has with "the churches" (see 3 John 12 for another example).
C. Paul's concern in this is that the gift being presented to the needy brothers and sisters in Jerusalem should be handled in such a way as to show forth "the glory of God" and the "ready mind" of the Corinthians (v. 19), and that in no way can anyone be blamed of wrongdoing (v. 20). These are things worth protecting. All of this was done in this earnest way so that "honorable things" can be provided—not only in the sight of God, but also in the sight of men (v. 21). It's not enough that we satisfy God with our integrity. God wants us to make sure that men are satisfied too.
III. THE PROVEN BROTHER SENT BY PAUL (v. 22).
A. In addition to Titus and this unnamed brother, Paul mentions another brother—also unnamed— that is from his own team (v. 22). He too has been proven diligent—not just once but many times. Integrity in the fulfillment of large responsibilities is first demonstrated through faithfulness in small things (Luke 16:10).
B. This was because of the great confidence Paul had in the Corinthians that they will faithfully follow through in all things. His sending this proven brother must have come as an encouragement to the Corinthians; but it was also to make sure that all things were done as they should be done (9:3-5).
IV. THE RESPONSIBILITY OF THE CHURCH (vv. 23-24).
A. Paul puts his own endorsement on the members of this visiting team (v. 23). He affirms Titus as his own partner and fellow worker in the work toward the Corinthians; and so they should receive him as they would receive Paul. And he also endorses the other brethren—both from the churches at large and from his own team—as "messengers" (literally "apostles"; that is, "sent ones") of the churches. Paul's reference to "the glory of Christ" may be with regard to the "messengers" (who live in such a way as to point to the glory of Christ), or the "churches" (in which Christ is glorified on earth).
B. In rightly receiving these members of an advanced accountability team, the church will show its own integrity. It will give proof of the love they had for Paul, and of Paul's rightness to boast in them (v. 24).