The incarnation of the Son of God in the person of Christ and His subsequent ministry, life, death, resurrection, and ascension all took place in actual history. This is the testimony of the New Testament—that God entered history to save His people from their sin. Yet, this does not mean the Lord was not working in history before the incarnation. In fact, He has been working in history from the very beginning.
Genesis 3:14–15 shows this to be the case. This passage, which Christian theologians have called the protoevangelium, or "first gospel," represents God's actual announcement in history of His plan of salvation. We cannot understand who Jesus is and what He came to do apart from understanding this text and how it is unfolded in the rest of Scripture.
Most of us are probably quite familiar with this text and its immediate context. Our Creator gave Adam and Eve everything they needed and more, even blessing them with His presence in Eden (Gen. 1–2). However, Adam and Eve betrayed God and ate from the forbidden tree, with the consequence of being alienated from Him (Gen. 3:1–13). The Lord would have been just to condemn them right away, and indeed, He did judge them for their sin (vv. 16–19). But God showed His grace in not judging Adam and Eve first. In a text loaded with cosmic significance, the Lord first curses the serpent—who is Satan (Rev. 12:9)—saying that his head will be bruised even as he bruises the heel of the seed of the woman (Gen. 3:14–15). This is nothing less than spiritual warfare instituted by our Maker. God promised His people that the devil would finally be defeated—he would suffer a crushing blow to the head—and that snakes crawl on the ground and lick the dust is a visible reminder of this fact.
The seed of the woman refers at the same time to both one and many individuals. It does not consist of every single descendant of Adam and Eve, for spiritually speaking, some people have a lineage that goes back to Satan (John 8:39–47). Those who are children of the devil are God's enemies; thus, those who are on the Lord's side are the seed of the woman who will defeat Satan. Still, given the fact that even God's friends are tainted by sin, we know that His people cannot be the seed that defeats the devil, at least not in and of themselves. Instead, the seed finds its ultimate fulfillment in Jesus, who defeated Satan on the cross (Col. 2:13–15). In Him, then, we find ourselves defeating the devil.
In Christ, our final defeat of Satan is assured, for Christ has already dealt the crushing blow. Satan's condition is terminal, and there is no chance that he will see victory. Yet just as the devil bruised Jesus on the cross, so he will endeavor to bruise us until he is cast into the lake of fire on that final day. Knowing this, we can prepare ourselves now to be faithful in suffering, looking to the Founder and Perfecter of our faith so that we will persevere when Satan attacks (Heb. 12:1–2).