In Matthew 22, when an expert in the Mosaic Law approached Jesus and asked which commandment is the greatest, Jesus summed up the the Law and the Prophets with the double-love command:
You shall love the Lord your God with all your heart and with all your soul and with all your mind. This is the first and great commandment. But the second is like it. You shall love your neighbor as yourself.
In Genesis 3, the man and woman proved that the first of the double-love command (to love God with all that we are) was too much for them. They loved things that were appealing to their eyes and appetite, things that were able to make them “wise,” more than they loved God.
In Genesis 4, Cain proved that the second part of the double-love command (to love our neighbor as we love our self) is out of our reach. Cain got mad. He was filled with rage and killed Abel. When the Lord asked, “Where is Abel,” just like his mother and father, he shirked his responsibility. “Am I my brother’s keeper” (Genesis 4:9) means “What? You expect me to look out for, take care of, and actually love my neighbor?”
According to Matthew, the Old Testament is summed up with the double-love command. But according to Luke 24, the OT can be summed up another way. Luke says the Law, Prophets, and Psalms point to Jesus himself. Half way through Genesis 4, the message of the Old Testament concerning Jesus and the double-love command is already clear. We’ve failed to love God and neighbor, and if we are to overcome the serpent and the effects of the fall, the “seed of the woman” (Gen 3:15) is going to have to come and crush both sin and the serpent.
Praise the Lord that he came, he finished the first part (John 19:30), and he is coming again to put an end to the serpent and the broken disorder in which we live.