Colossians 2:14, [Christ cancelled] the record of debt that stood against us with its legal demands. This He set aside, nailing it to the cross.
We all understand what it means to be in debt—to pay back money we borrowed that we did not have. Thus, it should be easy to fathom what it means to be spiritually bankrupt—to be in debt to the Devil for the many and various sins we committed against God since the moment of birth. This is a debt we cannot pay back, for it requires blood. Even if we paid the debt with our own blood, it would not be enough, hence the point of the near-sacrifice of Isaac (Genesis 22). The payment, then, requires an act of God.
That is just what Christ did—He performed the act of God by laying down His life to pay your sinful debt. Isaac’s life would not have been enough; the thousands—perhaps millions—of lambs and bulls sacrificed to God under the Old Testament (old covenant law) were not enough. Only the blood of God would suffice, which Christ gave for you and me. He nailed your debt to the cross, upon which it died with Him.
Therefore, the Law no longer applies to us insofar as salvation is concerned, for the Law requires perfect obedience—perfect payment—to be right with God, which we could not pay and do, and which Christ paid and did on our behalf. Hear, then, Luther’s comforting words:
Only Christ takes away the Law, kills my sin, destroys my death in His body, and in this way empties hell, judges the devil, crucifies him, and throws him down into hell. In other words, everything that once used to torment and oppress me Christ has set aside; He has disarmed it and made it in Himself (Colossians 2:14-15), so that it cannot dominate any longer but is compelled to serve me.
(Lectures on Galatians, 1535, LW 26:160-161)