Tertullian — Prescription against Heretics 2

Taking the similar case of fever, which is appointed a place among all other deadly and excruciating issues (of life) for destroying man: we are not surprised either that it exists, for there it is, or that it consumes man, for that is the purpose of its existence . In like manner, with respect to heresies , which are produced for the weakening and the extinction of faith , since we feel a dread because they have this power, we should first dread the fact of their existence ; for as long as they exist, they have their power; and as long as they have their power, they have their existence . But still fever, as being an evil both in its cause and in its power, as all know , we rather loathe than wonder at, and to the best of our power guard against, not having its extirpation in our power.

Some men prefer wondering at heresies , however, which bring with them eternal death and the heat of a stronger fire, for possessing this power, instead of avoiding their power when they have the means of escape: but heresies would have no power, if (men) would cease to wonder that they have such power. For it either happens that, while men wonder, they fall into a snare, or, because they are ensnared, they cherish their surprise, as if heresies were so powerful because of some truth which belonged to them. It would no doubt be a wonderful thing that evil should have any force of its own, were it not that heresies are strong in those persons who are not strong in faith .

In a combat of boxers and gladiators, generally speaking, it is not because a man is strong that he gains the victory, or loses it because he is not strong, but because he who is vanquished was a man of no strength; and indeed this very conqueror, when afterwards matched against a really powerful man, actually retires crest-fallen from the contest. In precisely the same way, heresies derive such strength as they have from the infirmities of individuals — having no strength whenever they encounter a really powerful faith .