1 Timothy 3:2

The existence of Church organization and presbyters at Ephesus is presupposed (Ti1 5:17, Ti1 5:19). The institution of Church widows (1Ti. 5:3-25) accords with this. The directions here to Timothy, the president or apostolic delegate, are as to filling up vacancies among the bishops and deacons, or adding to their number. New churches in the neighborhood also would require presbyters and deacons. Episcopacy was adopted in apostolic times as the most expedient form of government, being most nearly in accordance with Jewish institutions, and so offering the less obstruction through Jewish prejudices to the progress of Christianity. The synagogue was governed by presbyters, "elders" (Act 4:8; Act 24:1), called also bishops or overseers. Three among them presided as "rulers of the synagogue," answering to "bishops" in the modern sense [LIGHTFOOT, Hebrew and Talmudic Exercitations], and one among them took the lead. AMBROSE (in The Duties of the Clergy [2.13], as also BINGHAM [Ecclesiastical Antiquities, 2.11]) says, "They who are now called bishops were originally called apostles. But those who ruled the Church after the death of the apostles had not the testimony of miracles, and were in many respects inferior. Therefore they thought it not decent to assume to themselves the name of apostles; but dividing the names, they left to presbyters the name of the presbytery, and they themselves were called bishops." "Presbyter" refers to the rank; "bishop," to the office or function.

— Jamieson-Fausset-Brown Commentary (public domain)