22. 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" (1Co 4:17; 16:10), partly to convey his mind on various matters. After a brief stay he was to return (1Co 16:11). It is very unlikely that this Erastus was "the chamberlain of the city" of Corinth, of that name (Ro 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).

JFB.