“When you were dead in your sins and in the uncircumcision of your flesh, God made you alive with Christ. He forgave us all our sins, having canceled the charge of our legal indebtedness, which stood against us and condemned us; he has taken it away, nailing it to the cross. And having disarmed the powers and authorities, he made a public spectacle of them, triumphing over them by the cross.” (Colossians 2:13–15)

The reason that the union with Christ makes a great difference for the believer is that Christ achieved a decisive triumph over the devil at Calvary. He did not remove Satan from the world, but he disarmed him to the extent that the weapon of damnation was stripped from his hand.

He cannot accuse believers of unforgiven sin. Which is the only accusation that can destroy us. And therefore, he cannot bring us to utter ruin. He can hurt us physically and emotionally… He can tempt us and incite others against us. But he cannot destroy us.

The decisive triumph of Colossians 2:13–15 is owing to the fact that “the record of debt that stood against us” was nailed to the cross. The devil made that record his chief accusation against us. Now he has no accusation that can hold in the court of heaven. He is helpless to do the one thing he wants to do most: damn us. He can’t. Christ bore our damnation. The devil is disarmed.

Another way to say it is in Hebrews 2:14–15: “[Christ became human] that through death he might destroy the one who has the power of death, that is, the devil, and deliver all those who through fear of death were subject to lifelong slavery.”

From John Piper