V. A bishop must be no accepter of persons; neither revering nor flattering a rich man contrary to what is right, nor overlooking nor domineering over a poor man. For, says God to Moses, "Thou shalt not accept the person of the rich, nor shalt thou pity a poor man in his cause: for the judgment is the Lord's." [Leviticus 19:15 and Exodus 23:3] And again: "Thou shalt with exact justice follow that which is right." [Deuteronomy 1:17 and 16:20]
Let a bishop be frugal, and contented with a little in his meat and drink, that he may be ever in a sober frame, and disposed to instruct and admonish the ignorant; and let him not be costly in his diet, a pamperer of himself, given to pleasure, or fond of delicacies.
Let him be patient and gentle in his admonitions, well instructed himself, meditating in and diligently studying the Lord's books, and reading them frequently, that so he may be able carefully to interpret the Scriptures, expounding the gospel in correspondence with the prophets and with the law; and let the expositions from the law and the prophets correspond to the gospel. For the Lord Jesus says: "Search the Scriptures; for they are those which testify of me." [John 5:39] And again: "For Moses wrote of me." [John 4:46] But, above all, let him carefully distinguish between the original law and the additional precepts, and show which are the laws for believers, and which the bonds for the unbelievers, lest any should fall under those bonds. Be careful, therefore, O bishop, to study the word, that thou mayest be able to explain everything exactly, and that thou mayest copiously nourish thy people with much doctrine, and enlighten them with the light of the law; for God says: "Enlighten yourselves with the light of knowledge, while we have yet opportunity." [Hosea 10:12]
The above ancient advice is part of the so-called "Apostolic Constitutions," Book II, Section II, Paragraph V. Translation taken from Donaldson et al. (Edinburgh, 1870) "Ante-Nicene Christian Library: Translations of the Writings of the Fathers Down to A.D. 325," Volume XVII, page 29. Book II was actually translated by Rev. Thomas Smith, D.D. It's tough to date these "Constitutions," but the best guess would seem to be third or fourth century.
It is interesting to note the primary method for minister (bishop) to be taught is from studying the Bible.