“Cain received that instruction from God like a lawbreaker. For the fault of jealousy grew stronger, and he planned and carried out his brother’s murder. Such was the man who founded the earthly city. He also symbolizes the Jews by whom Christ was slain, the shepherd of the flock of men, who was prefigured in Abel, the shepherd of the flock of sheep.” [The City of God, 15.7]
Christ’s innocent sufferings were the climax of a long story of enmity between the Two Cities. Cain killed Abel, the descendents of Cain brought about great apostasy prior to the Flood, Pharaoh nearly killed Moses, Athaliah tried to kill newborn King Joash, Herod the Great sought the life of the newborn Christ, etc. Another way of putting this is that, ever since the Fall, there has been a battle between “two seeds” – the seed of the serpent and the seed of the woman (Gen. 3:14-15).
One of the most shocking things about the crucifixion of Christ is that the people of God became the seed of the serpent! Israel turned on God the Son and tried to exterminate Him. But in His death, which was the apparent victory of the seed of the serpent, the Serpent himself was crushed with a mortal wound. Jesus died as a substitute and would redeem His elect people from the grips of Satan, sin, and death.
Sin has infected the whole human race, even God’s people, making us all “the seed of the serpent” by nature. We think we know best and, therein, rebel against our heavenly King. But God has acted in Christ, who was born of a woman, born under the law, to redeem His elect from the Law’s curse. Christ won for Himself an eternal City.