Therefore whenever you hear of the kingdom of heaven, you should not merely gaze up to heaven, but look around you upon the earth and seek it among the people, in the whole world, where the Gospel is taught and Christ is believed in, and the Sacraments are properly used. The “kingdom of heaven,” in plain language, is the kingdom of Christ and the kingdom of the Gospel and of faith.

For wherever the Gospel is there Christ is also. And where Christ is there is the Holy Ghost also and His kingdom, the true kingdom of heaven. And all who have the Word and Sacraments and believe and remain in Christ by faith are heavenly princes and children of God. All that remains to be done is that God remove the partition which still separates us, that is, that we die, then all will be heaven and salvation.

Learn to understand then, in the first place, that the kingdom of heaven is the kingdom of our Lord Jesus and is to be found wherever the Word and faith are. In this kingdom we have life in hope and are, according to the Word and faith, cleansed from all sin and delivered from death and hell, notwithstanding the old Adam and the corruption of the flesh. The old Adam has not yet been destroyed and the sinful flesh has not been put away; this must yet be done, then there shall be nothing but life, righteousness and salvation. (Luther’s House Postil, Sermon for the Twentieth Sunday after Trinity, Volume 3, p. 843)

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)