Absolution, a Sacrament of repentance...

Furthermore, the Power of the Keys administers and presents the Gospel through Absolution, which is the true voice of the Gospel.  We also include Absolution when we speak of faith, because "faith comes from hearing," as Paul says in Romans 10:17.  When the Gospel is heard and the Absolution is heard, the conscience is encouraged and receives comfort.  Because God truly brings a person to life through the Word, the Keys truly forgive sins before God.  According to Luke 10:16, "The one who hears you hears Me."  Therefore, the voice of the one absolving must be believed no differently than we would believe a voice from heaven.  Absolution can properly be called a Sacrament of repentance, as even the more learned scholastic theologians say.  Meanwhile, in temptations this faith is nourished in a variety of ways: through the declaration of the Gospel and the use of the Sacraments.  For these are signs of the New Testament, that is, signs of the forgiveness of sins.  They offer the forgiveness of sins as the words of the Lord's Supper clearly testify, "This is My body, which is given for you.  This is the cup of the New Testament," and so on.  So faith is conceived and strengthened through Absolution, through the hearing of the Gospel, through the use of the Sacraments, so that it may not give in to the terrors of sin and death while it struggles.  This method of repentance is plain and clear.  It increases the worth of the Power of the Keys and of the Sacraments. It illumines Christ's benefit and teaches us to make use of Christ as Mediator and the Atoning Sacrifice.

~BOC, AP, XII (V), 39-43