פּירוש אויף בראשית 3:15

ואיבה אשית AND I WILL SET ENMITY — Your sole intention was that Adam should die by eating it first and that you should then take Eve for yourself (Genesis Rabbah 20:5), and you came to speak to Eve first only because women are easily influenced and know how to influence their husbands; therefore “I shall put enmity [between thee and the woman]”.

AND THOU SHALT BRUISE THEIR HEEL. This means man will have an advantage over you [the serpent] in the enmity between him and you for he will bruise your head but you will bruise him only in his heel, with which he will crush your brain.

ואיבה אשית, you, the serpent, made the woman feel as if you had her best interests at heart, as if you loved her; and as if your advice to her was motivated by love; I, G’d, will turn this love into hostility. בין זרעך ובין זרעה, between your offspring and between her offspring. The hostility between the serpent and the human species will not be an unalterable condition of life, seeing that in the Messianic era this enmity will be resolved and as we know from Isaiah 11,8 in those days an infant will suckle at its mother’s breast next to a snake’s lair without worrying.
הוא ישופך ראש, when he finds you he will smash your head whenever he is able to, whereas ואתה תשופנו עקב, when you slither along the ground on your belly and are unable to harm him higher up, you will bite his heel. The words ישופך and תשופנו describe inflicting of injury and smashing respectively, as we know from Job 9,17 אשר בשערה ישופני, “for he crushes me for a hair.” [with minimal provocation. Ed.] All of these verses are dealt with by the kabbalah, the interpretation of the text along mystical lines.