Office of the Keys
The authority Christ gave the church to forgive the sins of the repentant and to withhold forgiveness from the unrepentant. It appears in the Small Catechism as one of its parts, and it is why a Lutheran pastor's absolution is spoken as a declaration rather than a wish: not “I hope God forgives you” but “I forgive you all your sins.”
In Sacraments — Baptism, the Lord's Supper, confession, and the language around them.