This is what true repentance means. Here a persons 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 as you can be. 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. This must be believed. 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 (preceeding Christ) is called a preacher of repentance, but this is for the forgiveness of sins. That is, John was 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 [Mark 1:3] 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).
Smalcald Articles III III 3-6
From Treasury of Daily Prayer, Ash Wednesday, p. 25-26