2. The man, however, who would undertake their conversion, must possess an accurate knowledge of their systems or schemes of doctrine. For it is impossible for any one to heal the sick, if he has no knowledge of the disease of the patients. This was the reason that my predecessors—much superior men to myself, too—were unable, notwithstanding, to refute the Valentinians satisfactorily, because they were ignorant of these men's system; which I have with all care delivered to thee in the first book, in which I have also shown that their doctrine is a recapitulation of all the heretics. For which reason also, in the second, we have had, as in a mirror, a sight of their entire discomfiture. For they who oppose these men (the Valentinians) by the right method, do [thereby] oppose all who are of an evil mind; and they who overthrow them, do in fact overthrow every kind of heresy.