Whether any do inquire of Titus - It is to be observed that the words "any do inquire" are not in the original; nor is it clear that these are the most proper words to be introduced here. The Greek may mean either, "if any do inquire about Titus," or it may mean "if anything is to be said about Titus." The sense of the passage may either be, that some of the faction at Corinth might be disposed to inquire about the authority of Titus to engage in this work, or that Paul having said so much in commendation of the persons who went with Titus, it seemed proper also to say something in his favor also. The idea is, "If any inquiry is made from any quarter about him, or if it is necessary from any cause to say any thing about him, I would say he is my partner," etc.
He is my partner - He partakes with me in preaching the gospel, and in establishing and organizing churches; compare Titus 1:5. To the Corinthians this fact would be a sufficient commendation of Titus.
Or our brethren be inquired of - That is, the brethren who accompanied Titus. If any inquiry was made about their character, or if it was necessary to say anything in regard to them.
They are the messengers of the churches - They have the entire confidence of the churches, having been selected and appointed by them to a work of labor and responsibility; compare Philippians 2:25. The words here rendered "messengers of the churches," are in the original "apostles of the churches," (ἀπόστολοι ἐκκλησιῶν apostoloi ekklēsiōn). The word "apostles" here is used evidently in its proper sense, to denote one who is sent out to transact any business for others, or as an agent or legate. These persons were not apostles in the technical sense, and this is an instance where the word is applied in the New Testament to those who had no claim to the apostolic office. It is also applied in a similar way to Apollos and Barnabas, though neither, strictly speaking, were apostles.
And the glory of Christ - That is, they have a character so well known and established for piety; they are so eminent Christians and do such honor to the Christian name and calling, that they may be called the glory of Christ. It is an honor to Christ that he has called such persons into his church, and that he has so richly endowed them. Every Christian should so live as that it would appear to all the world that it was an honor and glory to the Redeemer that he had such followers; an honor to his gospel that it had converted such and brought them into his kingdom. It is sufficient honor, moreover, to any man to say that he is "the glory of Christ." Such a character should be, and will be, as it was here, a recommendation sufficient for any to secure them the confidence of others.

Whether any do inquire of Titus - Should it be asked, Who is this Titus? I answer, he is my companion, and my fellow laborer in reference to you; 2-Corinthians 2:13; 2-Corinthians 7:6, 2-Corinthians 7:7. Should any inquire, Who are these brethren, Luke and Apollos? I answer, They are Αποστολοι, apostles of the Churches, and intensely bent on promoting the glory of Christ.

Whether [any do enquire] of Titus, [he is] my partner and fellowhelper concerning you: or our (m) brethren [be enquired of, they are] the messengers of the churches, [and] the (n) glory of Christ.
(m) The two companions of Titus.
(n) By whom the glory of Christ is set forth.

Whether any do inquire of Titus,.... The apostle here sums up the characters of each of the above persons; as for Titus, he says,
he is my partner; he had been his companion in his travels, a partner with him in preaching the Gospel, as well as in the troubles and persecutions he had met with; and was one with whom he had had sweet communion and fellowship:
and fellow helper; or worker,
concerning you; he had been a joint instrument with him, either in their conversion, or consolation, and correction; or for their edification and instruction, and setting things right, which had been out of order among them:
or our brethren be inquired of; if their characters are asked after, as well as Titus's; by whom are meant not his fellow apostles, but the two brethren who were sent along with Titus; what may be truly said of them is,
they are the messengers of the churches; they were chosen and sent forth by the churches, not only to preach the Gospel, but particularly to take care of the ministration to the poor saints. They were messengers appointed by the churches for this service, and were also appointed to the service of the churches; respect seems to be had to the public minister in the synagogues, who was called "the messenger of the congregation", or "church" (z); whose business was to take care about the reading of the law and the prophets, to pray in public, and also to preach if there was no other; so we read (a) also of , "the messengers of the sanhedrim"; who were sent at the proper time to reap the sheaf of the first fruits, and of others who swore the high priest before the day of atonement (b); and of , "the messengers of the commandment" (c); who went to hear the exposition (of the traditions) and visit the head of the captivity:
and the glory of Christ: meaning either that the churches were the glory of Christ, in whom he is glorified, where his glory is seen, and his presence enjoyed; or rather the messengers of them, on whom the image of Christ was stamped, who faithfully performed the work of Christ, in all things sought his glory and not their own; and in and by whom his glory was displayed, and held forth to others.
(z) T. Bab. Sota, fol. 37. 2. Tosephot Beracot, fol. 34. 1. Misn. Beracot, c. 5. sect. 5. (a) Misn. Menachot, c. 10. 3. (b) Misn. Yoma, c. 1. 5. (c) T. Bab. Succa, fol. 26. 1.

fellow helper concerning you--Greek, "fellow worker towards you."
our brethren--the two mentioned in 2-Corinthians 8:18, 2-Corinthians 8:22.
messengers--rather, as the Greek, "apostles": in the less strict sense (Acts 14:14).
of the churches--sent by the churches, as we are by the Lord (Philippians 2:25). There was in the synagogue an ecclesiastical officer, called "the angel of the Church," whence the title seems derived (compare Revelation 2:1).

My partner - In my cares and labours. The glory of Christ - Signal instruments of advancing his glory.