Heresies, at the present time, will no less rend the church by their perversion of doctrine, than will Antichrist persecute her at that day by the cruelty of his attacks, except that persecution make seven martyrs, (but) heresy only apostates. And therefore “heresies must needs be in order that they which are approved might be made manifest,” both those who remained stedfast under persecution, and those who did not wander out of their way into heresy.
Tertullian
Against Marcion
The Prescription Against Heretics
Chapter IV