Thus only those sinners belong in the kingdom of Christ who recognize their sin, feel it, and then catch hold of the Word of Christ spoken here: “I do not condemn you.” These people constitute the membership of Christ’s kingdom. He admits no saint; He blows them all away; He expels from the church all who lay claim to holiness. If sinners enter, they do not remain sinners. He spreads His cloak over their sins and says: “If you have sinned, I remit your sins and cover them.” To be sure, sin is there. But the Lord in this kingdom closes His eyes to it, covers it, forgives it, and does not impute it to the sinner. So a living saint and member of Christ stands here, made out of an adulteress who had been infested with sin but whose sin is now forgiven and covered. Even if sinners are knaves and criminals, their sins will be forgiven, as long as they feel them, repent of them, and ask God for forgiveness. If you have tasted the Law and sin, and if you know the ache of sin, then look here, and see how sweet, in comparison, the grace of God is, the grace which is offered to us in the Gospel. This is the absolution which the adulteress receives here from the Lord Christ.
Luther’s Works, Volume 23, page 318