Gaius mine host - Who has received me into his house, and shown me hospitality. The word "host" means one who entertains another at his own house without reward.
And of the whole church - Who has opened his house to entertain "all" Christians; or to show hospitality to them all. He was baptized by Paul himself at Corinth 1-Corinthians 1:14; and was so highly esteemed by the church that John wrote an epistle to him; 3-John 1:1. He was probably a wealthy citizen of Corinth, who freely opened his house to entertain Christians, and for the purpose of religious worship.
Erastus - Erastus is mentioned Acts 19:22 as having been sent by Paul with Timothy into Macedonia. He is also mentioned 2-Timothy 4:20 as having resided at Corinth.
The chamberlain - A chamberlain is properly an officer who has charge of a chamber, or of chambers. In England, the lord chamberlain is the sixth officer of the crown, and has charge of the king's lodgings, and wardrobe, etc. He has also an important rank on days of public solemnities, as the coronation day, etc. The word used here is commonly in the New Testament translated "steward." It properly means one who has charge of domestic affairs, to provide for a family, to pay the servants, etc. In this place it means one who presided over the pecuniary affairs of the "city," and should have been translated "the treasurer; the city treasurer;" an once of trust and of some importance, showing that, "all" who were converted at Corinth were not of the lowest rank. This is implied in 1-Corinthians 1:26, "Not many wise men, not many mighty, not many noble, are called," implying that there were some such.
Quartus a brother - A fellow-Christian.

Gaius mine host - Gaius in Greek is the same as Caius in Latin, which was a very common name among the Romans. St. Luke (Acts 19:29) mentions one Gaius of Macedonia, who was exposed to much violence at Ephesus in the tumult excited by Demetrius the silversmith against St. Paul and his companions; and it is very possible that this was the same person. He is here called not only the host ξενος, the entertainer of St. Paul, or Tertius, (if he wrote this and the following verse), but also of the whole Church: that is, he received and lodged the apostles who came from different places, as well as the messengers of the Churches. All made his house their home; and he must have been a person of considerable property to be able to bear this expense; and of much piety and love to the cause of Christ, else he had not employed that property in this way.
Erastus the chamberlain of the city - Treasurer of the city of Corinth, from which St. Paul wrote this epistle. This is supposed to be the same person as is mentioned Acts 19:22. He was one of St. Paul's companions, and, as appears from 2-Timothy 4:20, was left about this time by the apostle at Corinth. He is called the chamberlain οικονομος, which signifies the same as treasurer; he to whom the receipt and expenditure of the public money were intrusted. He received the tolls, customs, etc., belonging to the city, and out of them paid the public expenses. Such persons were in very high credit; and if Erastus was at this time treasurer, it would appear that Christianity was then in considerable repute in Corinth. But if the Erastus of the Acts was the same with the Erastus mentioned here, it is not likely that he now held the office, for this could not at all comport with his travelling with St. Paul. Hence several, both ancients and moderns, who believe the identity of the persons, suppose that Erastus was not now treasurer, but that having formerly been so he still retained the title. Chrysostom thought that he still retained the employment.
Quartus a brother - Whether the brother of Erastus or of Tertius we know not; probably nothing more is meant than that he was a Christian - one of the heavenly family, a brother in the Lord.

Gaius mine host,.... There was one Gaius a Macedonian, that was with the apostle at Ephesus, Acts 19:29; and another Gaius of Derbe, that accompanied him into Asia, Acts 20:4; whether either of these, as the latter seems more probable, was this person, is not certain. However, it seems very likely that it is the same Gaius the apostle baptized at Corinth, 1-Corinthians 1:14; and some have thought him to be the same that the Apostle John wrote his third epistle to, and indeed the characters of hospitality and generosity there given him well agree with this, who was not only the apostle's host that entertained him in a kind and liberal manner, but of all the saints:
and of the whole church, saluteth you; that is, of the church at Corinth, to whom he was kind and hospitable, even to as many as stood in need of his assistance; or of the church of Christ in general, being beneficent and liberal to all Christian strangers that came that way, lodged them at his house, and provided every thing proper and convenient for them. Dr. Lightfoot thinks that there was a public hospital or receptacle for strangers at Corinth, in imitation of the Jews, who had a place adjoining to their synagogues to entertain travellers in; and that Gaius was the chief officer and overseer of this house, who, discharging his trust well, is deservedly commended. That the Jews had places near their synagogues for such a purpose is, certain. It is said (b),
"why do they sanctify (or consecrate the day?) that travellers may do their duty, who eat, and drink, and sleep in the synagogue.''
The gloss on it is,
"not the synagogue itself, but the chambers which were near the synagogue, are called the synagogue, and from thence they heard the consecration.''
And elsewhere (c) it is said,
"in the synagogues they neither eat nor drink--but there is a place near the synagogue where travellers used to sleep and eat;''
and then follows what is said before. And Maimonides (d) observes,
"there is no sanctification (of the sabbath) but in the place where the meal is eaten; so a man may not sanctify in one house, and eat in another; but if he sanctifies in this, he must eat in this; but why do they sanctify in the synagogue? because of travellers who eat and drink there.''
Upon which his commentator remarks (e), that
"they do not eat in the synagogue at all, but they eat, , "in a house near the synagogue", where they sit at the time of hearing the sanctification.''
But whether there was such an house at Corinth near the place of public worship, or any where else for this purpose, is not certain; and to make Gains only an overseer over such an house, though a faithful one, greatly sinks his character; since one would conclude from hence, that his entertainment of the apostle, and other saints, was at his own expense.
Erastus the chamberlain of the city saluteth you; whom the apostle is said to leave at Corinth, 2-Timothy 4:20, and at another time to send along with Timotheus into Macedonia, if the same person is intended; for these do not seem so well to accord with his being in such an office, which must require attendance, and would not admit of going from place to place with the apostle, or of being sent by him. The city, of which he was chamberlain, was the city of Corinth, where the apostle and this Erastus were, when this epistle was wrote. The word translated "chamberlain", is often used for a steward; and here it signifies such an officer as had the care of the city chest or coffer, and distributed the public money; and seems to answer to the "quaestor urbanus", or city treasurer, among the Romans, whose business it was to receive the city accounts, and disburse at all occasions of public expenses; so that this was a place of honour and trust; hence it appears, that though not many, yet some rich and honourable were called by grace, and embraced the Gospel. His name signifies beloved, and is the same with David in Hebrew. What nation he was of is not certain, whether a Roman, a Greek, or Jew; one of this name is reckoned among the seventy disciples, and it said to be bishop of Paneas, or of the Philippians; See Gill on Luke 10:1.
Quartus a brother; not of Tertius, nor of Erastus, nor of the apostle according to the flesh, as some have thought, but a brother in a spiritual relation. This man, as appears from his name, was a Roman; probably had before lived at Rome, and therefore sends his salutations to the Christians there: he is mentioned among the seventy disciples, and said to be bishop of Berytus; See Gill on Luke 10:1.
(b) T. Bab. Pesachim, fol. 101. 1. (c) Gloss. in T. Bab. Bava Bathra, fol. 3. 2. (d) Hilchot Sabbat, c. 29. sect. 8. (e) Maggid. Misnah in ib.

Gaius mine host, and--the host
of the whole church--(See Acts 20:4). It would appear that he was one of only two persons whom Paul baptized with his own hand (compare 3-John 1:1). His Christian hospitality appears to have been something uncommon.
Erastus the chamberlain--"treasurer."
of the city--doubtless of Corinth. (See Acts 19:22; 2-Timothy 4:20).
and Quartus a brother--rather, "the" or "our brother"; as Sosthenes and Timothy are called (1-Corinthians 1:1; 2-Corinthians 1:1, Greek). Nothing more is known of this Quartus.

The chamberlain of the city - Of Corinth.