All now depends on this, that you accept such assurance and hold it to be true that God is merciful unto you for Christ’s sake. This we here learn from the man sick with the palsy. In the first place, the Lord admonishes him to believe, saying: Son, be of good cheer, and doubt not, thy sins are forgiven thee. As soon as the palsied man believed these words his sins were really forgiven.

Thus we come into possession of the forgiveness of sins in our day also, when the servant of the Church, or any other Christian, assures you: God is not angry with you, do not you be angry with Him, because He has, for the sake of His Son Jesus Christ, forgiven you all your sins. You should therefore, with all confidence, trust in this assurance and suffer yourself to be torn to pieces rather than to doubt it. For if you doubt, the absolution, even if it were pronounced over you orally by God and His holy angels, would profit you nothing.

Where there is no faith, there God is considered a liar, as though He did not tell us the truth and would not fulfill His promises. May God in mercy graciously deliver us from such unbelief and sin, although the devil is a real expert in leading people to consider God a liar and to distrust His promises. (Luther’s House Postil, Sermon for the Nineteenth Sunday after Trinity, Volume 3, p. 832)

This Gospel teaches us to note particularly the good tidings which God has granted us, that we may here on earth say to each other, “Thy sins are forgiven thee,” so that with the people here spoken of we may marvel and glorify God, Which had given such power unto men. And it is indeed a great power that one Christian may say to another: My brother, be of good cheer, you have a gracious God; only believe the assurance which I give you in Christ’s name and it is as certain as if God Himself had said to you, Thy sins are forgiven thee. Such power, as we hear, originated in Christ and is now given unto men, especially to those who are in office and are commanded to preach the Gospel, that is, repentance and forgiveness of sins, in Jesus’ name. Other Christians, although they are not in that office, also have the command, in case of necessity, to comfort you when you are troubled on account of your sins, and to say: Why are you troubled? I, as a Christian, assure you that you are wronging yourself; God is not unmerciful unto you. You are for Christ’s sake to put all your trust in His grace. You are to comfort yourself as surely with these words as if Christ spake them in person from heaven. (Luther’s House Postil, Sermon for the Nineteenth Sunday after Trinity, Volume 3, p. 831-832)