Dr. Martin Luther continues his commentary on Deuteronomy 18 verse 15: “The Lord Your God will raise up for You a prophet like me from among You, from Your brethren – Him You shall heed” – translated by Richard R. Caemmerer in Luther´s Works Volume 9, pages 176-180:

This is the chief passage in this whole book and a clearly expressed prophecy of Christ as the new Teacher. Hence the apostles also courageously adduce this passage (Acts 3:22–23; Acts 7:37). Appropriately, Moses places it here at the end, after he has finished his discourses concerning the priesthood, the kingdom, the government, and the whole worship of God. It is his purpose to show that in the future there will be another priesthood, another kingdom, another worship of God, and another word, by which all of Moses will be set aside. Here Moses clearly describes his own end, and he yields his mastery to the Prophet who is to come. Let us therefore examine his words rather carefully.
First, it is necessary for this Prophet to bring a new word, a word which Moses has not taught, because here God promises that He will put words into His mouth. But if this were not another word, there would be no need to promise that it will be brought by this Prophet; it would have been enough to say: “He shall be a mouth for you,” just as is said of Aaron in Ex. 4:16, which would mean that the Prophet would teach the words of Moses and his written Law. Now when he says: “Heed Him who will be raised up like me,” he teaches plainly that his own word is different from the Word of that Prophet. And this he confirms when he says that the people on Mt. Sinai demanded such a prophet to speak to them, since they had already heard the whole Law through Moses.
But there cannot be another word beyond the word of Moses, unless it is the Gospel, since everything that belongs to the teaching of the Law has been transmitted most perfectly and amply by Moses, so that nothing further can be added. For what could be added to the Decalog, to say nothing of the rest? What loftier thing can be taught than to believe, trust, love, and fear God with one’s whole heart, not to tempt God, etc.? Furthermore, what rules can be more just and holy than those which Moses ordains concerning the external worship of God, government, and love for one’s neighbor? Therefore the Jews have no cause here to gabble that this Prophet will be one who interprets Moses. Moses interprets himself in this book so well that there is no need of another; nor can another add one jot or tittle to make him clearer or more perfect. Since, therefore, there cannot be another word beyond the perfect teaching of the Law unless it were the Word of grace, it follows that this Prophet will not be a teacher of the Law but a minister of grace. Thus this text clearly forces the Jews to expect from this Prophet something other than what they have in Moses.
Secondly, unless that new Prophet were to bring another word, Moses would not need to compare Him to himself when he says: “The Lord will raise Him up, like me.” All the other prophets who taught Moses and did not raise up another word were not like Moses or similar to Moses but inferior to Moses, namely, servants of the word of Moses, teaching what Moses had commanded. Therefore in all of them the people did not hear anyone else or themselves; they heard Moses himself and his words. For Moses speaks in them and puts his words into their mouths, and they are his mouth to the people. This Prophet, however, he does not dare subordinate to himself and put his words into His mouth; but he says that He will be like him in service and obedience, by which he certainly excludes Him from obedience to him and places Him above all prophets who taught on the basis of Moses.
But to exclude Him from obedience to Moses and to prefer Him above all prophets teaching on the basis of Moses is to affirm positively that the ministry of the Law is to be ended and a new one to be set up, since no man is free from the service of the Law but all are subject to the Law. Therefore it is necessary that this Prophet, who is like Moses—in respect to authority of teaching and commanding, that is, for this is what he means when he says “like me”—be superior to Moses and teach greater things. Unless He were greater than Moses, Moses would not yield obedience and authority to Him. Moreover, unless He taught greater things, He could not be greater. He is not speaking here of similarity between Moses and that Prophet in regard to personal worth but of similarity in authority or office. He is not dealing here with the life, morals, or deeds of Moses and this Prophet but with doctrine, as the text sufficiently proves; for a prophet is a prophet because he teaches and comes to teach, and here the command is to “heed Him.”
If, therefore, the doctrine of both is considered, it will be easily apparent from the comparison of their doctrine what He must preach. Moses is a minister of the Law, sin, and death; for he teaches and stresses works, and through the rays of the Law he makes everyone guilty of death and subject to punishment for sin. He demands, but he does not give what he demands. However, since this Prophet finds Moses teaching this and is Himself set up as a Teacher next to him, His Word must teach something else. But He cannot teach anything else than sin, wrath, and death unless He teaches righteousness, grace, and life. Therefore it is necessary that He be a teacher of life, grace, and righteousness, just as Moses is a teacher of sin, wrath, and death. But both teachings must be heard just as they have been raised up by God; for through the Law all must be humbled, and through the Gospel all must be exalted. They are alike in divine authority, but with respect to the fruit of their ministry they are unlike and completely opposed to each other. The sin and wrath which Moses arouses through his ministry that Prophet cancels through righteousness and grace by His ministry. This Prophet, therefore, demands nothing; but He grants what Moses demands.
In this passage we have those two ministries of the Word which are necessary for the salvation of the human race: the ministry of the Law and the ministry of the Gospel, one for death and the other for life. They are indeed alike if you are looking at their authority, but most unlike if you are thinking about their fruit. The ministry of Moses is temporary, finally to be ended by the coming of the ministry of Christ, as he says here, “Heed Him.” But the ministry of Christ will be ended by nothing else, since it brings eternal righteousness and “puts an end to sin,” as it is said in Dan. 9:24. Therefore the Levitical priesthood is wholly ended here and set aside, because it was established to teach Moses. But if the priesthood is ended, the Law is also ended, as it is said (Heb. 7:12): “When there is a change in the priesthood, there is necessarily a change in the Law as well.” Thus this Prophet can be none other than Christ Himself.
From all this it follows how completely foreign and even pestilential those teachers in the New Testament are who trouble consciences with laws and works, when this prophecy concerning Christ totally wipes out and does away with that ministry. Even more pestilential are those who weary the earth with their traditions and human laws. If the ministry of this new Prophet does not endure the Law of Moses, which is divine, how will it endure the laws of men in His kingdom? You see, therefore, that by this one text the whole chaos of papistic tyranny, together with its monks, is completely upset.
But here you will say: “You will find commands everywhere in the gospels and the epistles of the apostles. Therefore either our Christ will not be this Prophet, or His doctrine will not differ at all from the Law of Moses.” To reply briefly: The commands of the New Testament are directed to those who are justified and are new men in the Spirit. Nothing is taught or commanded there except what pertains solely to believers, who do everything spontaneously, not from necessity or contrary to their own will. But the Law is directed to the old man, who is dead in sin, to urge him on and to show him his sin. This is the true and proper teaching of the Law. Therefore the Law finds man not only unwilling but also unable to do what the Law demands. Thus he says here in the text that on the day of the assembly the people refused and could not hear the voice of the Law, and that therefore they asked for another teacher, one who would speak to them a word they could bear.
The understanding of this matter lies in recognizing and truly distinguishing the Law and the Gospel, that you may know that the teaching of the Law commands only what is to be done by the ungodly and lost, as 1 Tim. 1:9 says: “The Law is not laid down for the just but for the lawless.” But where the godly are, there the Law, which is intended only for the humiliation of the ungodly through the recognition of their sin and weakness, is already abolished. The Gospel teaches from what source you receive the power to fulfill the Law. In this respect it commands nothing; nor does it force the spirit, which hastens of its own accord by faith. It adds some commands, but it does so to kill the remnants of the old man in the flesh, which is not yet justified. From these commands, however, the spirit is free, being satisfied with faith alone. Of this matter we have spoken amply elsewhere.
Now let us look at the words: “The Lord your God will raise up for you a Prophet like me from among you, from your brethren—Him you shall heed.” Here he prophesies that Christ will be true man and will come from the blood of the Jews, because salvation is from the Jews (John 4:22). No one has ever arisen from this people who taught a different word from the word of Moses and set up a new ministry except this one Christ of ours. However many prophets there were before Him, they all preserved and taught Moses. This Prophet freed not only the Jews from Moses but all nations throughout the world and gave them the new Word of the Gospel. That He was from the Jews, both the Gentiles and the Jews being witnesses, proves that it is He of whom Moses speaks here, and that this prophecy is fulfilled in Him.