DEUT327 Destroy the seven nations. The seven nations were the ones that introduced to the world all sorts of idol-worship, as well as all of the other abominations that Hashem hates. Since they were the center of idol-worship and they introduced it, we were commanded to annihilate them and leave no trace of them under the heavens. None were to be left among the living, and all remembrance of them was to be obliterated. This mitzvah was to serve a benefit, that having annihilated these nations, the Jewish People would never follow in their ways. Also, by fiercely attacking them and chasing after them to kill them because of their idol worship, we would take a lesson and no Jew, even for a moment, would think to imitate these nations, for any reason in the world.