Let us, therefore, learn to be brave in all perils, especially, however, against ourselves and our heart. For there Satan has a most firm seat and is supported especially by the past. For he knows that we are sinners, therefore he holds the succession of our sins and the sad “bond” (Col. 2:14) before our eyes and oppresses us. Yea, he seizes also upon present things and opposes us with them, for example, that we do not yet believe as firmly as we ought, do not yet love so warmly, and are also tempted with impatience. When he magnifies these things - for he is a cunning and vehement speaker - the heart is broken and terrified not only by that tumult of princes and kings, but even by the rustle of a falling leaf.
We should, therefore, fortify our hearts and look toward the invisible things and into the depths of the Word. We should not fear and quake at what we feel within or outside of us that is sensible and visible and is perceived by the flesh. We should lay aside our senses and go where the present verse leads us, to things invisible. And when Satan reproaches you: “Behold, you are a sinner, you do not believe, you do not love as the Word requires”; you say against this: “Why do you plague me with these visible things? I perceive these things well. Nor is it necessary for you to teach me. This is necessary, that I follow the Word and direct myself to invisible things, that is, to Him who dwells in the heavens and to His Word. In His eyes all things which terrify me are a mere jest and trivial spectacles of the flesh, as they are called, which are arranged not for terror, but for laughter.”
This verse must be applied in this way, not only to these external perils which are stretched out threateningly against us by the enemies of the Word, by the Turk, the pope, the bishops, kings, princes, by all who have been provided with power, wisdom, and righteousness, but also to spiritual temptations, when the devil terrifies the conscience, accusing us within ourselves on accounted of the sins we have committed. He, then, who has rightly reflected on this verse will laugh at Satan as well as at his accusations and threats. He will say: “These things are nothing to me, which even move my God, who dwells in heaven, to laughter. You will not prevail with your accusing and gloom-spreading, nay, rather, I also shall laugh with my God, for I know that your attempts are vain. For even if I am a sinner, even if the punishment of sin is eternal death, this will not keep me from laughing. For at the right hand of God sits He who made satisfaction for sins and conquered you in His own flesh and overthrew you. You assail not me alone, but Him who vanquished you, the Son of God.”
We must firmly believe that all persecutions, even that spiritual persecution which through Satan takes place in our hearts, occurs for the sake of Christ. For to believe in the forgiveness of sins through Christ is the highest article of our faith. And it is true that whoever believes this article has the forgiveness of sins. Therefore Satan tries so greatly to tear this faith from us.
Luther’s Works, AE
Vol 12 pp. 25, 26, 27