Genèse 3:15

And I will put enmity between thee and the woman, and between the seed of thy son, and the seed of her sons; and it shall be when the sons of the woman keep the commandments of the law, they will be prepared to smite thee upon thy head; but when they forsake the commandments of the law, thou wilt be ready to wound them in their heel. Nevertheless for them there shall be a medicine, but for thee there will be no medicine; and they shall make a remedy for the heel in the days of the King Meshiha.

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, woman would henceforth be an object of disgust even in her own estimation, as described in the Talmud (Shabbat 152) “although a woman is a vessel full of excrement and her orifice full of blood,” (men run after her as if she was the most desirable creature) This was going to be the relationship between males and females in the future, not only that between Adam and Chavah [who apparently could not bring himself to have intercourse with her for the next 130 years. Ed.]

ובין זרעך ובין זרעה, not only between Adam and Chavah, but also between their respective male and female offspring.

הוא ישופך ראש, these thoughts crossing man’s mind will reduce the satisfaction he obtains already in the early stages of sexual intercourse, a feeling gradually reinforced when he considers the potential harm he may cause himself by indulging in copulation, diminishing both the qualitative and quantitative enjoyment of it.

ואתה תשופנו עקב, he who initially derives pleasure from his superiority will eventually cause himself harm at the end of the pleasure cycle.

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.