I Tertius, who wrote this epistle
This name is a Latin one, and perhaps the person might be a Roman, for the names Secundus, Tertius, Quartus, Quintus were common with the Romans; unless it may be thought, as it is by some, that this man was the same with Silas, who was a constant companion of the apostle; and the Hebrew word (vlv) is the same as Tertius; he also is numbered among the seventy disciples, and said to be bishop of Iconium; (See Gill on Luke 10:1). Whosoever he was, it is certain he was an amanuensis of the apostle, who wrote this letter, either from the apostle's notes, or from his mouth.
Salute you in the Lord.
Some connect this phrase, "in the Lord", with the other, "wrote this epistle", and make the sense to be that he wrote this epistle for the Lord's sake, for his honour and glory; which he might do, though he wrote it not by inspiration, being only scribe to the apostle; but it is better connected with the word "salute", and the sense is, that his salutation was not a mere form, nor only concerned their temporal good, but their spiritual welfare; that he wished them well in the Lord, that they might have much communion with him, and larger measures of grace from him.