Josh 8:22

“You will read in the Holy Scriptures about the battles of the just ones, about the slaughter and carnage of murderers, and that the saints spare none of their deeply rooted enemies. If they do spare them, they are even charged with sin, just as Saul was charged because he had preserved the life of Agag king of Amalek. You should understand the wars of the just by the method I set forth above, that these wars are waged by them against sin. But how will the just ones endure if they reserve even a little bit of sin? Therefore, this is said of them: "They did not leave behind even one who might be saved or might escape."Do you perhaps not believe me that the battle is joined against our sin? Then believe Paul as he says, "Not yet to the shedding of blood have you resisted against sin." Do you see that the fight proposed for you is against sin and that you must complete the battle even to the shedding of blood? Is it not evident that the divine Scripture indicates these things, even as it habitually says, "Sanctify war," and, "You will fight the battle of the Lord"?”

“When the Jews read these things, they become cruel and thirst after human blood, thinking that even holy persons so struck those who were living in Ai that not one of them was left "who might be saved or who might escape." They do not understand that mysteries are dimly shadowed in these words and that they more truly indicate to us that we ought not to leave any of those demons deeply within, whose dwelling place is chaos and who rule in the abyss, but to destroy them all. We slay demons, but we do not annihilate their essence. For their work and endeavor is to cause persons to sin. If we sin, they have life; but if we do not sin, they are destroyed. Therefore, all holy persons kill the inhabitants of Ai; they both annihilate and do not release any of them. These are doubtless those who guard their heart with all diligence so that evil thoughts do not proceed from it, and those who heed their mouth, so that "no evil word" proceeds from it. Not to leave any who flee means this: when no evil word escapes them.”