One of the greatest struggles in the Christian life is that against the torment and accusation of sin. Those without a well-developed understanding of the great horrors of sin are sometimes free from this burden, but others can be tormented by their sins to the point of despair. I admit, I tend to gravitate toward despair…and therefore, I find great comfort in these words of Luther. Writing on 2 Cor 5.21, he says:
When you become aware of your sin and frightened by it, you must not allow the sin to remain in your conscience. This would only lead to despair. Rather, just as your awareness of sin flowed to you from Christ, so you must pour your sin back on him to free your conscience.
So be careful you don’t become like the misguided people who allow their sin to bite at them and eat at their hearts. They strive to rid themselves of this sin by running around doing good works. But you have a way to get rid of your sins. You throw your sins on Christ when you firmly believe that Christ’s wounds and suffering carried and paid for your sins. As Isaiah said, “The LORD has laid on him the iniquity of us all” (Is 53.6). Peter said Christ himself “bore our sins in his body on the tree” (1 Pet 2.24). And Paul said, “God made him who had no sin to be sin for us” (2 Cor 5.21).
You must rely on these and similar verses with your whole heart. The more your conscience torments you, the more you must rely on them. For if you don’t do this and try to quiet your conscience through your own sorrow and penance, you will never find peace of mind and will finally despair in the end. If you try to deal with sin in your conscience, let it remain there, and continue to look at it in your heart, your sins will become too strong for you. They will seem to live forever. But when you think of your sins as being on Christ and boldly believe that he conquered them through his resurrection, then they are dead and gone. Sin can’t remain on Christ. His resurrection swallowed up sin.
(from Faith Alone: A Daily Devotional /LW 42:12)