Therefore one should hold fast to this comfort, that what God has once declared, this He does not change. You were baptized, and in Baptism the kingdom of God was promised you. You should know that this is His unchangeable Word, and you should not permit yourself to be drawn away from it. For although it can happen—as with those who were on the way to Emmaus (Luke 24:28)—that He pretends to want to go farther and seems to be dealing with us as though He had forgotten His promises, faith in the Word must nevertheless be retained, and the promise must be stressed—namely, that it is true and dependable—even if the manner, time, occasion, place, and other particulars are unknown. For the fact that God cannot lie is sure and dependable.
Luther, M. (1999, c1964). Vol. 4: Luther’s works, vol. 4 : Lectures on Genesis: Chapters 21-25 (J. J. Pelikan, H. C. Oswald & H. T. Lehmann, Ed.). Luther’s Works (4:96). Saint Louis: Concordia Publishing House.