Timotheus - Timothy. He was a proper person to send there to visit the churches, as he had been there before with Paul, when they were established, Acts 16:3; Acts 17:14.
And Erastus - Erastus was chamberlain of Corinth (Romans 16:23), or, more properly, the treasurer of the city (see the notes on that place), and he was, therefore, a very proper person to be sent with Timothy for the purpose of making the collection for the poor at Jerusalem. Paul had wisdom enough to employ a man accustomed to monied transactions in making a collection. On this collection his heart was intent, and he afterward went up with it to Jerusalem. See 2-Corinthians 8:9, and notes on Romans 15:25-26.
Stayed in Asia - At Ephesus.
For a season - How long is uncertain. He waited for a convenient opportunity to follow them, probably intending to do it as soon as they had fully prepared the way for the collection. See Paley's Horae Paulinae, p. 1, chapter 2.

So he sent into Macedonia - He desired Timothy to go as far as Corinth, 1-Corinthians 4:18, and after that to return to him at Ephesus, 1-Corinthians 16:11; but he himself continued in Asia some time longer; probably to make collections for the poor saints in Jerusalem. Erastus, mentioned here for the first time, appears to have been the chamberlain, οικονομος, either of Ephesus or Corinth; see Romans 16:23. He was one of St. Paul's companions, and is mentioned as being left by the apostle at Corinth, 2-Timothy 4:20.

So he sent into Macedonia,.... To Philippi, or Thessalonica, or Berea, or some of the places there, to let them know of his coming, and to prepare for him:
two of them that ministered unto him; that were his assistants in preaching the Gospel:
Timotheus and Erastus; the former of these was a disciple he found at Lystra, and took along with him, and to whom he afterwards wrote two epistles; and the latter seems to be the same with him, who was chamberlain of the city of Corinth, and is said to abide there, Romans 16:23 The Ethiopic version, instead of Erastus, wrongly reads Aristarchus; whereas it is certain, he was not sent into Macedonia, but was with the apostle at Ephesus in the tumult, Acts 19:29.
But he himself stayed in Asia for a season; that is, at Ephesus, as the following narration shows.

So he sent into Macedonia . . . Timotheus and Erastus--as his pioneers, in part to bring "them into remembrance of his ways which were in Christ" (1-Corinthians 4:17; 1-Corinthians 16:10), partly to convey his mind on various matters. After a brief stay he was to return (1-Corinthians 16:11). It is very unlikely that this Erastus was "the chamberlain of the city" of Corinth, of that name (Romans 16:23).
he himself stayed in--the province of
Asia for a season--that is, at Ephesus, its chief city. (Asia is mentioned in contrast with Macedonia in the previous clause).