But what if a bishop, if a deacon, if a widow, if a virgin, if a doctor, if even a martyr, have fallen from the rule (of faith), will heresies on that account appear to possess the truth? Do we prove the faith by the persons, or the persons by the faith? No one is wise, no one is faithful, no one excels in dignity, but the Christian; and no one is a Christian but he who perseveres even to the end.
Tertullian
Against Marcion
The Prescription Against Heretics
Chapter III