13. Who does not see the necessity that the evil should be separated from the good, lest the latter should be infected with the contagion of deadly evil, and perish? For evil, inasmuch as it is implanted in human nature by birth, and is more and more ingenerated in children from parents when the church is advancing towards consummation, is like the malignant disease which is called cancer, which spreads round about, and gradually mortifies the healthy and living parts. What husbandman, or gardener, when he sees briars, nettles, thorns, and thistles growing, does not extirpate them before he sows and harrows in his corn and food crops? What farmer, when he sees his herbage and grass consumed by worms, or locusts, does not dig a ditch, and separate the green field from the wasted one, and thus take treasures for the preservation of his crops and green fields? What shepherd, when he sees wild beasts multiplying about the pastures of his sheep, does not call together the neighboring shepherds and the servants, and with weapons, or traps, kill those wild beasts, or drive them away? [2] What king, when he sees both the towns of his kingdom round about his metropolis taken by enemies, and the property of his subjects taken possession of by them, does not assemble the troops and cast out the enemy, and restore the stolen goods to their owners, and, moreover, add thereto the spoils of the enemies wealth, and so comfort them?