"And I will put enmity between you and the woman, and between your seed and her Seed; He shall bruise your head, and you shall bruise His heel." (New King James Version).
The context of this prophecy is the original sin and fall of Adam and Eve in the Garden of Eden.
There are three parts to this great prophecy. Part number one:
God is talking to Satan and God is telling him that from this point on there is going to be enmity, i.e., war. From that time forth there will be two kingdoms: the kingdom of God and the kingdom of the devil and they are still in conflict to this day. All Christians are in the kingdom of heaven (Gospel of Mark uses kingdom of God, but it is the same thing). The kingdom of the devil will be filled with his followers as seen in John 8:44 when Jesus tells the ungodly, "You are of your father the devil . . . "
Part number two:
The war will be between Satan's followers and "her Seed." Who is "her" and who is the "Seed?" The "her" is the virgin Mary. Galatians 4:4 tells us, "But when the fullness of the time had come, God sent forth His Son, born of a woman . . . " Please notice the "Seed" is capitalized. In the NKJV of the Bible, all deity is capitalized to present clarity and avoid confusion. Also fascinating is that "seed" throughout the Bible is almost always referring to the man. I believe that this is the only verse that refers the seed to that of a woman. The "Seed" refers to the Messiah, Jesus Christ the Redeemer. Jesus will be the "Second Adam" and correct the mistake that the first Adam made.
Part number three:
"He shall bruise your head, and you shall bruise His heel." Satan bruised the heel of Jesus on the cross. However, when Jesus rose from the grave, He bruised (crushed) Satan's head. Satan was defeated at the cross and his doom is predicted explicitly in Revelation 20:10, "The devil, who deceived them, was cast into the lake of fire . . . "
Due to Adam and Eve's fall from grace, their dominion of "every living thing that moves on the earth (Genesis 1:28) which God had given them authority over, was taken by Satan. Paul refers to Satan as the "god of this world" many times, e.g., II Corinthians 2:4.
To make this even more thorough, examine the "Temptations of Christ" found in Luke, especially Luke 4:5-6, "Then the devil, taking Him up on a high mountain, showed Him all the kingdoms of the world in a moment of time. And the devil said to Him, "All this authority I will give You, and their glory; for this has been delivered to me, and I give it to whomever I wish." So, who delivered all this authority to Satan? It sure was not God. Satan took it from Adam and Eve at their fall from grace when original sin came into the world.
Now, the coup de gras is delivered in Matthew 28:18, when Jesus, after resurrecting from the dead and immediately before ascending to heaven, says His last words on earth, which is called the Great Commission, " . . . All authority has been given to Me in heaven and on earth . . . " That means the devil has none. Jesus, as the second Adam, has taken back the authority that the first Adam had lost.
And so, what we have here is the first prophecy in which God promises to us the eventual defeat of Satan which would come from Eve's descendents. Our Redeemer lives. We know how all of this ends. And to Jesus goes all the power and glory, forever and ever.