Second Council of Nicaea, Canon II

That he who is to be ordained a Bishop must be steadfastly resolved to observe the canons, otherwise he shall not be ordained.

When we recite the psalter, we promise God:  “I will meditate upon thy statutes, and will not forget thy words.”  It is a salutary thing for all Christians to observe this, but it is especially incumbent upon those who have received the sacerdotal dignity.  Therefore we decree, that every one who is raised to the rank of the episcopate shall know the psalter by heart, so that from it he may admonish and instruct all the clergy who are subject to him.  And diligent examination shall be made by the metropolitan whether he be zealously inclined to read diligently, and not merely now and then, the sacred canons, the holy Gospel, and the book of the divine Apostle, and all other divine Scripture; and whether he lives according to God’s commandments, and also teaches the same to his people.  For the special treasure (οὐσία) of our high priesthood is the oracles which have been divinely delivered to us, that is the true science of the Divine Scriptures, as says Dionysius the Great.  And if his mind be not set, and even glad, so to do and teach, let him not be ordained.  For says God by the prophet, “Thou hast rejected knowledge, I will also reject thee, that thou shalt be no priest to me.”

Translation: Henry R. Percival, The Seven Ecumenical Councils, NPNF II.14 (1900), via CCEL.