Christ completely renewed all things, both taking up the battle against our enemy and crushing him who at the beginning had led us captive in Adam, trampling on his head, as you find in Genesis that God said to the serpent, “I will put enmity between you and the woman, and between your seed and the seed of the woman. He will be on the watch for your head, and you will be on the watch for his heel.” From then on it was proclaimed that he who was to be born of a virgin, after the likeness of Adam, would be on the watch for the serpent’s head. This is the seed of which the apostle says in the letter to the Galatians, “The law of works was established until the seed should come to whom the promise was made.” He shows this still more clearly in the same epistle when he says, “But when the fullness of time was come, God sent his Son, made of a woman.” The enemy would not have been justly conquered unless it had been a man made of woman who conquered him. For it was by a woman that he had power over man from the beginning, setting himself up in opposition to man. Because of this the Lord also declares himself to be the Son of Man, so renewing in himself that primal man from whom the formation of man by woman began, that as our race went down to death by a man who overcame, and as death won the palm of victory over us by a man, so we might by a man receive the palm of victory over death.
"You are more cursed than all cattle because you deceived those who have authority over all cattle; and instead of being more astute than all other animals you shall be more cursed than all other animals, and you shall go about on your belly because you brought pangs upon womankind. And you shall eat dust all the days of your life [ Gen. 3:14 ] because you deprived Adam and Eve of the food of the Tree of Life. And I will place enmity between you and the woman, and between your seed and her seed [ Gen. 3:15 ] because by your fraudulent show of love you deceived and subjected both her and her children to death.
He then indicates the nature of the enmity which was placed between the serpent and the woman, between its seed and hers, saying, "It shall tread upon your head--which wanted to escape from subjugation to her seed--and you will strike it, not in its organ of hearing, but in its heel. " [ Gen. 3:15 ]
God judged that evil was to be held in check for a time rather than to be destroyed, so that he says to the serpent, “I will put enmity between you and the woman, and between your seed and the seed of the woman. She shall watch for your head and you for her heel.” Where enmities remain, there remains discord and the desire to do harm. Where there is the desire to do harm, there evil is established. Therefore there is discord between the serpent and the woman. Evil is at the base of discord; thus evil has not been taken away. Indeed, it has been reserved for the serpent, that he might watch for the woman’s heel and the heel of her seed, so as to do harm and infuse his poison. Therefore let us not walk in earthly things, and the serpent will not be able to harm us. Let us put on sandals of the gospel that shut out the serpent’s poison and blunt his bites that we may be provided with covering on our feet by the gospel.
(Verse 15) He himself will keep your head, and you will keep his heel. It is better in Hebrew: He will crush your head, and you will crush his heel; for our steps are hindered by the serpent, and the Lord will quickly crush Satan under our feet.
Enmities are not set between the serpent and the man but between the serpent and the woman. This is surely not because he fails to deceive and tempt men, is it? On the contrary, it is clear that he does deceive them. Or is it because he did not deceive Adam but his woman? But is the serpent then not the enemy of the man to whom that deception came through his woman, especially since “I will place enmity between you and the woman” is stated in the future? If the reason is that he did not thereafter deceive Adam, it is also true that he did not thereafter deceive Eve. Hence, why does Scripture put it this way? To show clearly that we cannot be tempted by the devil except through that animal part, which reveals, so to speak, the image or exemplification of the woman in the one whole man.
I will put enmity between you and the woman, and between your seed and her seed. The seed of the woman is the entire human race, the seed of the devil are the betrayers, who are depraved with his example of pride and rebellion. His seed is a perverse suggestion; the seed of the woman is the fruit of good work, by which the perverse suggestion is resisted. The enmity mentioned between this serpent and his seed, and how much the human race endures this enmity, and how much enmity all the elect exercise against him by living rightly, is clearer than the sun to all the faithful. A sign of this enmity appears even in the nature of the irrational serpent, which, because of the innate pestilence of its venom, exists always as an enemy to all living creatures and beasts of the earth: it is to be believed that from the time of this curse, and not before, this was implanted in it.
She will crush your head, and you will lie in wait for her heel. The woman crushes the head of the serpent, when the holy Church detects and scatters the devil’s wiles and toxic suggestions from the very start, and as if trampling on him, reduces him to nothing. She crushes the serpent's head when she resists the pride through which Eve was deceived, often humbling under God’s mighty hand: for the beginning of all sin is pride. The serpent lies in wait for her heel, because the devil, circling around the Church like a roaring lion, seeks whom he may devour, how he may overthrow the steps of our good actions. He lies in wait for the heel, when he tries to snatch us at the end of this present life. For the heel, which is the end of the body, not unjustly designates the end of our life, which both are also figuratively announced by the condition of the serpent, who is accustomed to be crushed by all who have the power, and he himself does not cease lying in wait to strike the heels of men.
[AD 202] Irenaeus on Genesis 3:15