In similar fashion to that of Stuart Robinson, Geerhardus Vos, explained the meaning of Genesis 3:15 in redemptive-history–tracing the various parts of the promise in order to show the Christological nature of it–when he wrote:
40. Where is the covenant of grace first revealed?
In the mother promise, Gen 3:15, “I will put enmity between you and this woman, and between your seed and her seed. It will crush your head and you will crush its heel.” Some have disputed that we are dealing with a covenant here. It must be conceded that the formal conclusion of a covenant is lacking, which, moreover, would have been incomprehensible to Adam and Eve. Only later, when the idea of a covenant had developed on natural terrain, God Himself used the term with Noah and Abraham, etc. But as far as the essence of the matter is concerned, the covenant was certainly with Adam since that mother promise. It was a protevangelium, a “first gospel,” and the gospel is in itself a revelation of the covenant of grace. One should note the following:
a) Through a powerful word, God establishes enmity between the seed of the serpent and that of the woman, between the serpent and the woman herself. He thereby creates a relationship. This agrees completely with the manner in which He always acts in the realization of His covenant. Later, He says to Abraham, “I institute,” “I establish,” “I give my covenant.”
b) Enmity between the woman and her seed, on the one hand, and the serpent and its seed, on the other, points to a relationship of friendship with God. After all, man had renounced friendship with God and had allied himself with Satan. Where friendship with Satan has now turned into enmity, this can mean nothing other than that friendship with God has been restored. So here the covenant relationship is clearly included.
c) It has been rightly noted that the promise of sanctifying grace was also included in this promise. How else could enmity have arisen where friendship existed? God Himself must reverse the situation through re-creating grace. He apparently worked at the same time, or already before that time, in the hearts of Adam and Eve, adding the grace of the covenant to the gospel of the covenant.
d)When God thus, through His omnipotence, brings about enmity against Satan in man, then this includes that God chooses man’s side; expressed in our current language, that He becomes man’s ally in the conflict against the serpent. An offensive and defensive covenant is present here in substance, although one should acknowledge that Adam could not immediately have clearly understood this relationship. In fact, this did not also need to be the case immediately. The protevangelium was not only there for the initial moment; it was there as a treasure to be preserved and pondered.
e) This relationship between God and man on one side and Satan on the other is a relationship that is not limited to individuals, but extends to the seed. And that is an essential element of the covenant concept, as we have already seen more than once. The covenant encompasses the generations. Here, too, that is true. It does not extend only to the woman, but to the woman’s seed. Adam and Eve were instructed by this how this enmity against Satan, which God graciously willed to work in them, would also continue in their posterity. There would be a never-broken line of fighters against the serpent.
f)In opposition, however, there will also be a seed of the serpent. It is not a conflict against the serpent in himself, but also against the followers whom the serpent will acquire among men. In this, one finds expressed that the covenant of grace is particular, that it draws a dividing line through humanity, and that not all are reckoned as the seed of the woman to whom the promise extends. And here, too, there is a certain bond—it is a seed of the serpent.
g) The conflict that was established by God’s powerful word between the woman’s seed and the serpent will not remain unresolved. Indeed, the serpent shall crush the heel of the woman’s seed. And, conversely, the woman’s seed shall crush the serpent’s head. Therein is present, in principle, the doctrine of the atonement. The evil one and the power of evil can be overcome only if they are permitted to harm their foes. It had to be permitted that the serpent wound the woman’s seed in the heel. The serpent has to bite His heel and so pour the poison of death into Him, so that He becomes the serpent lifted up (John 3:14–15). But just because the serpent strikes at His heel with its bite, He has been given the opportunity to bring down His heel on its head. It can strike Him only from below, that is, in such a position that it becomes possible for Him to kill it when it bites. This is linked to the curse pronounced on it: “On your belly you shall go, and you shall eat dust all the days of your life” [Gen 3:14]. Because sin is cursed, the serpent can kill, but because it kills from the power of a curse and not by a blind law of nature, the possibility exists that killing by sin becomes the killing of sin. Since the serpent bites in the heel from the earth, it can be pushed down into the earth by the heel of the Serpent Trampler and crushed.
h) Among the seed of the woman we understand not only, but certainly in the deepest sense, Christ. He is the seed of the woman, as He was the seed of Abraham. In Him, all who are at enmity with the serpent have their unity. In fact, it was already not the natural seed in the wider sense that was meant by the seed of the woman. It was the spiritual seed that would not be the serpent’s seed. And as Paul says (in Gal 3) that Abraham’s seed consisted partly in believers and partly in Christ, without the one excluding the other, so it will also be here. In a deeper sense, only the natural descendants of the woman are the true seed of the woman, since they belong to Christ. And Christ is also in a literal sense the seed of the woman. In order to triumph in the conflict against the serpent, He had to be born from a woman, from the mother of all living, and share in our human nature, and at the same time be more than man. After all, it was a conflict not against human powers, but against the serpent, thus against a higher, spiritual, demonic power that must be crushed here. Clearly the evil one is in the background.
The fact that our ancestors did not understand all this in detail is not relevant. But without doubt they would have grasped the heart of the matter. And no one with an eye for this protevangelium can deny that, in its substance, the covenant of grace was already present in paradise.1
1. Vos, G. (2013). Reformed Dogmatics. (A. Godbehere, R. van Ijken, K. Batteau, D. van der Kraan, & H. Boonstra, Trans., R. B. Gaffin & R. de Witt, Eds.) (Vol. 2, pp. 73–75). Bellingham, WA: Lexham Press.