[For] true repentance a person needs to hear something like this, "You are all of no account, whether you are obvious sinners or saints ‹in your own opinions›. You have to become different from what you are now. You have to act differently than you are now acting, whether you are as great, wise, powerful, and holy. Here no one is godly."
But to this office of the Law, the New Testament immediately adds the consoling promise of grace through the Gospel. As Christ declares, "Repent and believe in the gospel" (Mark 1:15). That is, become different, act differently, and believe My promise. John the Baptist is called a preacher of repentance for the forgiveness of sins. That is, John was to accuse all and convict them of being sinners. This is so they can know what they are before God and acknowledge that they are lost. So they can be prepared for the Lord to receive grace and to expect and accept from Him the forgiveness of sins. This is what Christ Himself says, "Repentance and forgiveness of sins should be proclaimed in [My] name to all nations" (Luke 24:47).
The Law without the Gospel, is death and hell, and one must despair. St. Paul says, the Law kills. On the other hand, the Gospel brings consolation and forgiveness through the Word and the Sacraments. As Psalm 130:7 says, "with the Lord is…plentiful redemption." (paragraphs 3-8)
Condensed from CONCORDIA: THE LUTHERAN CONFESSIONS, copyright 2005,2006 by Concordia Publishing House. Used by permission. All rights reserved. To purchase a copy of CONCORDIA, call 800-325-3040.