The snake is cursed, for the education of Man. (God speaks to it as ה’ אלקים – see Names of God for more )
From this point forward there is hatred between snakes and people. Perhaps this is to always remind Man that he must keep away from “animal wisdom.” Man must not follow his instinct but rather exercise his free will to follow God’s commands.
God tells the snake, which represents the voice of the animal lust that tempts Man, Man will hit you on the head and you will hit him on his heel. By this God is telling Man that he is stronger than his evil inclination. Man can do more harm to the snake than the snake can to Man (when Man is ready to fight the fight).
When Man is off guard, his evil inclination can get the best of him, just as a snake quickly jumps out and bites man.
Additionally, when Man arouses his lusts, he falls to them. When he leaves them to slumber, he can overcome them.
Beraishis 3:14-15, Pages 81-82
