William Burkitt on 2 Timothy 4:20

Erastus is mentioned, Rom 16:23 as chamberlain of the city of Corinth, one that shewed kindness to Paul; he was a great man, the treasurer of the city of Corinth; yet neither his riches, nor his great place, could keep him from loving the apostle and the afflicted church of God. Rarely are great men good, and as rarely are good men great; yet some great men are good, and some good men are great. Lot and Abraham, Job and David were full of riches, yet full of piety, under the Old Testament: So was Nicodemus, Joseph of Arimathea, and Zaccheus, under the New. Thus God magnifies the power of converting grace. - Trophimus have I left at Miletum sick. This man was a citizen at Ephesus, a disciple and companion of St. Paul, whom he was forced to leave sick at Miletum. Acts 20:4

Note, Strength of grace cannot prevail against bodily weaknesses and diseases; sickness may seize even the best men.

Note also, That the apostles had not the gift of healing, when they pleased, but only when God gave it them.