105. Thy Word is a lamp to my feet and a light to my paths. A wonderful statement! Why not a lamp to my eyes and a light for seeing? Can the feet be lighted or the paths see? But the nature of faith for this life is expressed. For eyes must be taken captive to the obedience of Christ and be led by the Word alone, which is perceived by the ears and is not seen with the eyes. For we believe the invisible but not the inaudible. Therefore the Word does not enlighten the eyes, but neither the ears. Yet it is a lamp, because it guides the feet and the heart, and faith does not require understanding. Not understanding, but willing, not knowing but doing, what is heard is the right thing. And you will not go astray if you believe and go, even though you do not see. Only walk securely in what you have heard, because His Word will be a lamp to your feet and a light for your paths. Nothing is required except that you do what you do not know, perform what you do not understand, go where you do not know [the way], following the leading of the Word, and become foolish, dismissing your own thought. As if you followed the leader in the dark on a way you do not know, and you say to the leader: “Very well, You are the light of my feet but not of my eyes, because I see nothing, and yet I walk straight, as if I were seeing. I go astray and do not know where I am, and yet my feet certainly go the right way, as if they saw the light.” Thus faith does not enlighten the understanding, indeed, it blinds it, but rather the heart. Faith leads it where it will be saved, and it does so through the hearing of the Word. The heart, hearing the Word, begins to walk after it, not knowing where. Therefore the Word of God, which gives light to the feet and the paths, is wonderful. Not so the word of the letter and of human wisdom, which empties faith, because it makes faith understand what it says and because it shows itself to be a lamp to the eyes. Then it is not free not to say, “a lamp for the paths and a light to the feet.” For the Word encloses the light as the lamp does the candle, and this for the feet. But for the paths the light is not thus enclosed. Why this? Unless the faith of the beginner is at first less bright and more closed to the mind, like a lamp. But when you have begun to walk and to do what you believe, then the way is recognized more clearly than your feet recognize it, so that you have the light more brightly as a result of doing than as a result of believing with the heart alone. For while you believe, you have the light shut up in the heart, but when you act, then you will be led correctly on the way by the light that has now, as it were, been brought out. The doers are much more enlightened in faith than the speculative, as even the philosopher says in his Metaphysics, that an experienced person acts more surely.
Luther’s works, vol. 11: First Lectures 2