"Turn back to God and you will receive forgiveness for your sins..."
The people were promised that the moment they repented of their sins, God would blot out, wash away, or forgive their sin. They would be cleansed, given a new slate, as it were, so that a new message could be written about their lives. Imagine with me for a moment, you are in the courtroom, there is the list of charges. You are guilty of 140 counts of failures and mistakes. But in a sweeping moment, each of those charges is wiped away, and in their place stands a new list of perfect and right actions (the righteousness of Christ)!
What would you think and feel in that moment?