4:19 Paul sent greetings to his old friends Prisca (Priscilla) and Aquila who then lived in Ephesus (cf. Acts 18:2, 18, 26; Rom. 16:3; 1 Cor. 16:19). He also greeted the loyal family of Onesiphorus of whom he had written earlier (1:16).
4:20 Erastus and Trophimus were old associates of Timothy (Acts 19:22; 20:4; 21:29). Paul sent news of them. Some authorities believe that Paul's ability to heal people physically had ended. Many of them believe that God gave the gift of healing to the church only in its infancy to help authenticate the apostles as they ministered to the Jews (Eph. 2:20; Heb. 2:3-4).98A better explanation, I think, is that, though the gift of healing did decline, Jesus' and the apostles' ability to heal always depended on the sovereign will of God (Luke 5:17; Acts 3:12-13). Evidently it was not God's will for Trophimus to experience miraculous healing then.
4:21 Winter severely restricted travel in some parts of the Roman world. Timothy needed to leave Ephesus soon so he could reach Rome without undue difficulty. Paul relayed the greetings of four other brethren, probably local, whom Timothy evidently knew, as well as the greetings of all the local Christians.
"Linus is mentioned by Irenaeus (Against Heresies, iii.3) as the first bishop of Rome after the death of Peter and Paul."99
