Thus this is written for our instruction and comfort, in order that we may learn to pray with full confidence and not to despair or have any doubt about being heard. Although prayer is offered contrary to and beyond understanding, yet it is not unavailing; for God does not want us to insult Him by thinking that He is not truthful. And this is why He has told us to pray. He has not only commanded us to do so; but He has also promised that He will hear, in order that we might maintain with assurance that He wants to grant what we are asking for. Therefore it is the highest type of religion and worship to believe that God is truthful. Besides, we have a simple and definite form in which He has prescribed what we should pray for and how this should be done. Therefore if you pray: “Our Father, etc.,” think: “Thou, O Lord, hast told me to pray and hast promised that Thou wilt hear him who prays.” Nor should you have any doubts about God’s truth and promises. Even if the devil were to overturn the entire world in a single moment, the name of God will nevertheless be hallowed. And even if we all had to die, yet we are undoubtedly preserved and watched over for the future resurrection. Indeed, we see the manifest power and efficacy of our prayer; for the government of the world is surely preserved through prayer, our life is preserved, and all the good things we enjoy in this world are preserved.
Luther’s works, vol. 4: Lectures on Genesis: Chapters 21-25 p 366