St. Antony sought knowledge from every available source. That was his first quality as a student. He did not seek knowledge just from great teachers, but from everything and everybody, from every event, every person and even from sinners.

He learned his first lesson from a dead man. Isn’t it amazing that he gets his first lesson in monasticism not from a living person but from a dead man, and that dead man was his father? When his father died he looked at his body and learned something from it. He looked at his dead father who owned 300 acres of the best farm land in upper Egypt and who had the wealth, power, and influence and said, “Where is your power, your greatness and your might? You have departed from this world not by your choice; I however, will leave it by my choice before I am forced out.” That was his first lesson about dying to the world. “Behold that great rich man filling the world with power and influence, now lies motionless with no control over his own body!”

—H.H. Pope Shenouda III, Contemplations on the Life of St. Antony the Great

Remember that the Lord is in every Christian. When your neighbor comes to you, always have great respect for him, because the Lord is in him, and often expresses His will through him. ‘It is God which worketh in you both to will and to do of His good pleasure’ (Phil. 2:13). Therefore, do not grudge anything to your brother, but do unto him as unto the Lord; especially as you do not know in whom the Lord will come and visit you; be impartial to all, be kind to all, sincere and hospitable. Remember that sometimes God speaks even through unbelievers, or disposes their hearts towards us, as it happened in Egypt when the Lord gave Joseph favor in the sight of the keeper of the prison. (Gen. 39:21).

—St. John of Kronstadt, My Life in Christ

So those who wish to live virtuously should not hanker after praise, be involved with too many people, keep going out, or abuse others (however much they deserve it), or talk excessively, even if they can speak well on every subject.

—St. Diadochus

Be faithful in what you know, that you may be entrusted with more. Distrust your intellect, which has so often misled you. My own has been such a deceiver, that I no longer count upon it.

—François Fénelon, Spiritual Progress

St. Mark, in his new reply to these statements, repeats the Orthodox view that “it is possible for one to be a Teacher and all the same not say everything absolutely correctly, for what need then would the Fathers have had for Ecumenical Councils?—and such private teachings (as opposed to the infallible Scripture and Church Tradition) “we must not believe absolutely or accept without investigation.” He then goes into great detail, with many citations from his works, to show that St. Gregory of Nyssa actually did teach the error ascribed to him (which is nothing less than the denial of eternal torment in hell, and universal salvation), and gives the final authoritative word on this matter to Augustine himself. 

“That only the canonical Scriptures have infallibility is testified by Blessed Augustine in the words which he writes to Jerome: ‘It is fitting to bestow such honor and veneration only to the books of Scripture which are called “canonical,” for I absolutely believe that none of the authors who wrote them erred in anything…. As for other writings, no matter how great was the excellence of their authors in sanctity and learning, in reading them I do not accept their teaching as true solely on the basis that they thus wrote and thought.‘ Then, in a letter to Fortunatus [St. Mark continues in his citations of Augustine] he writes the following: ‘We should not hold the judgment of a man, even though this man might have been orthodox and had a high reputation, as the same kind of authority as the canonical Scriptures, to the extent of considering it inadmissible for us, out of the reverence we owe such men, to disapprove and reject something in their writing if we should happen to discover that they taught other than the truth which, with God’s help, has been attained by others or by ourselves. This is how I am with regard to the writings of other men; and I desire that the reader will act thus with regard to my writings also.”

(St. Mark, “Second Homily on Purgatorial Fire,” chs. 15-16; Pogodin, pp. 127-32).The Place of Blessed Augustine in the Orthodox Church by Fr. Seraphim Rose

Wisdom is much broader than intelligence; intelligence is a mere fragment of wisdom. A person may possess extraordinary intelligence yet does not behave wisely.

—H.H. Pope Shenouda III, Characteristics of the Spiritual Path