Christ redeemed us from the curse of the law by becoming a curse for us—for it is written, “Cursed is everyone who is hanged on a tree.” Galatians 3:13
God put [Christ] forward as a propitiation by his blood, to be received by faith. This was to show God’s righteousness, because in his divine forbearance he had passed over former sins. Romans 3:25
In this is love, not that we have loved God but that he loved us and sent his Son to be the propitiation for our sins. 1 John 4:10
If God were not just, there would be no demand for his Son to suffer and die. And if God were not loving, there would be no willingness for his Son to suffer and die. But God is both just and loving. Therefore his love is willing to meet the demands of his justice.
God’s law demanded, “You shall love the LORD your God with all your heart and with all your soul and with all your might” (Deuteronomy 6:5). But we have all loved other things more. This is what sin is—dishonoring God by preferring other things over him, and acting on those preferences. Therefore, the Bible says, “All have sinned and fall short of the glory of God” (Romans 3:23). We glorify what we enjoy most. And it isn’t God.
Therefore sin is not small, because it is not against a small Sovereign. The seriousness of an insult rises with the dignity of the one insulted. The Creator of the universe is infinitely worthy of respect and admiration and loyalty. Therefore, failure to love him is not trivial—it is treason. It defames God and destroys human happiness.
Since God is just, he does not sweep these crimes under the rug of the universe. He feels a holy wrath against them. They deserve to be punished, and he has made this clear: “For the wages of sin is death” (Romans 6:23). “The soul who sins shall die” (Ezekiel 18:4). There is a holy curse hanging over all sin. Not to punish would be unjust. The demeaning of God would be endorsed. A lie would reign at the core of reality. Therefore, God says, “Cursed be everyone who does not abide by all things written in the Book of the Law, and do them” (Galatians 3:10; Deuteronomy 27:26).
But the love of God does not rest with the curse that hangs over all sinful humanity. He is not content to show wrath, no matter how holy it is. Therefore God sends his own Son to absorb his wrath and bear the curse for all who trust him. “Christ redeemed us from the curse of the law by becoming a curse for us” (Galatians 3:13).
This is the meaning of the word “propitiation” in the text quoted above (Romans 3:25). It refers to the removal of God’s wrath by providing a substitute. The substitute is provided by God himself. The substitute, Jesus Christ, does not just cancel the wrath; he absorbs it and diverts it from us to himself. God’s wrath is just, and it was spent, not withdrawn. Let us not trifle with God or trivialize his love. We will never stand in awe of being loved by God until we reckon with the seriousness of our sin and the justice of his wrath against us. But when, by grace, we waken to our unworthiness, then we may look at the suffering and death of Christ and say, “In this is love, not that we have loved God but that he loved us and sent his Son to be the [wrath-absorbing] propitiation for our sins” (1 John 4:10).
John Piper, Fifty Reasons Why Jesus Died Chapter 1