Erastus abode at Corinth - He was treasurer of that city, as we learn from Romans 16:23 (note). The apostle had sent him and Timothy on a mission to Macedonia, Acts 19:22, whence it is probable he returned to Corinth, and there became finally settled.

Trophimus have I left at Miletum sick - Even the apostles could not work miracles when they pleased; that power was but rarely given, and that for very special purposes. Trophimus was an Ephesian. See Acts 20:4, and the note there.

Miletus was a maritime town of Ionia, not far from Ephesus; but there was another Miletus, in Crete, which some learned men think to be intended here. It appears that St. Paul went from Macedonia to Corinth, where he left Erastus; from Corinth he proceeded to Troas, where he lodged with Carpus: from Troas he went to Ephesus, where he visited Timothy; from Ephesus he went to Miletus, where he left Trophimus sick; and having embarked at Miletus, he went by sea to Rome. See Calmet. It is most likely, therefore, that the Miletus of Ionia is the place intended.

Erastus.

Acts 19:22 So he sent into Macedonia two of them that ministered to him, Timotheus and Erastus; but he himself stayed in Asia for a season.

Romans 16:23 Gaius my host, and of the whole church, salutes you. Erastus the chamberlain of the city salutes you, and Quartus a brother.

Trophimus.

Acts 20:4 And there accompanied him into Asia Sopater of Berea; and of the Thessalonians, Aristarchus and Secundus; and Gaius of Derbe...

Acts 21:29 (For they had seen before with him in the city Trophimus an Ephesian, whom they supposed that Paul had brought into the temple.)

Miletum.

Acts 20:15,17 And we sailed there, and came the next day over against Chios; and the next day we arrived at Samos, and tarried at Trogyllium...

Miletus. sick.

Philippians 2:26,27 For he longed after you all, and was full of heaviness, because that you had heard that he had been sick...

Demas
BY REV. PRINCIPAL DAVID ROWLANDS, B.A. Many a man who figures in history, is only known in connection with some stupendous fault--some mistake, some folly, or some sin--that has given him an unenviable immortality. Mention his name, and the huge blot by which his memory is besmirched starts up before the mind in all its hideousness. Take Cain, for example. He occupies the foremost rank as regards fame; his name is one of the first that children learn to lisp; and yet what do we know about him? …
George Milligan—Men of the Bible; Some Lesser-Known

The Glory of Jesus and Mary.
Before entering upon the contemplation of the excellent glory which surrounds the blessed in heaven, we must endeavor to form a correct idea of God's grace, which enabled them to perform the great and noble actions we are now to consider. They were all, except Jesus and Mary, conceived in sin, and, therefore, subject to the same temptations that daily assail us. They never could have triumphed and reached the supernatural glory which now surrounds them, had they been left to their own natural strength, …
F. J. Boudreaux—The Happiness of Heaven

Exhortation to Workers and Ministers
In conclusion I feel that the Lord would be pleased for me to say a few words for the encouragement of young ministers and workers. In my work in the ministry I have come through many varied experiences that, I trust, will be helpful to you in the trials through which you will have to pass before you get settled in the Lord's work. The first difficulty met by most young ministers and workers is in regard to their call. Unless the call be clear and definite, they are likely to be in some doubt as …
Mary Cole—Trials and Triumphs of Faith