Dr. Martin Luther continues his commentary on Deuteronomy with this summary of chapter 12 – and it´s good reading in this translation by Richard R. Caemmerer in Luther´s Works Volume 9, pages 123-126:
The spiritual explanation of the First Commandment has been finished, and the heart has been instructed. Moses now moves on to works and the outward worship of God in action and ceremonies.
And first he issues a decree concerning the place of divine worship; he repeats about five or six times that they should sacrifice and worship God, not in any place that pleases them but only in the place which the Lord chooses. Then he also commands that the places, the altars, and the statues of the Gentiles be wrecked and their memory erased.
When the general and constant place for the continual sacrifice of the whole people was being spoken of, the place chosen by God was wherever the Ark of the Covenant and the tabernacle were. Otherwise He often chose another place for one day or year, as is apparent in Samuel, Elijah, Gideon, Manoah and others; but He did so by a special revelation either through an angel or through a prophet.
All this He commands in order that in the worship of God the people may not be carried away by its own feeling, however holy and good, but may be governed by the Word; for if man does not live without the Word even with respect to the belly, how much less does he live without the Word in the work of God and in the spirit!
God wants our conscience to be certain and sure that it is pleasing to Him. This cannot be done if the conscience is led by its own feeling, but only if it relies on the Word of God.
Therefore if they should worship God in a place chosen by themselves, even if they pleased themselves thereby, nevertheless they would not be sure that they were pleasing God. They were sure that they were pleasing Him only if they made offerings in a place set apart through the Word of God.Page 123
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.Page 125