Memorable among the statements of this chapter are these two: “You shall not do according to all that we are doing here this day, every man doing whatever is right in his own eyes” (v. 8), and, “Everything that I command you you shall be careful to do; you shall not add to it or take from it” (v. 32). The former wholly condemns free will. It compares our efforts with the Word of God, inasmuch as by a general statement it wants us to choose and accomplish nothing unless the Word of God goes before us and lights the way. Thus no other place should be chosen, etc. From this it follows that whatever we attempt without the Word is sheer darkness and error. If this were not the case, it would not have been necessary to warn us not to do what seems right to us; nor would we be in need of the Word. The latter statement removes presumption, lest we do things that are better than the Lord commands; and at the same time it gives us liberty and absolves us of all works, efforts, laws, and traditions of men; and it binds our consciences to the Word of God alone. Of this very much elsewhere.
Luther’s works, vol. 9: Lectures on Deuteronomy 1525