Deuteronomy 18:15-20, the First Reading for the 4th Sunday after Epiphany in the Year of Mark, is matched very well with the Gospel Reading which centers on Jesus' emergence as the bringer of a "new teaching". In this brief passage we hear Moses declare that God will raise up a new prophet and this one shall speak "everything that [the Lord] command[s]." This new prophet is also an answer to prayer, according to Moses. It is clearly, then, an act of grace. It will be the preacher's task to make this clear to the listener.
(The following questions are meant to probe a fundamental question for Law and Gospel preachers, i.e. how does the Word function in the text? These questions are not meant to stand alone, but are best used in conjunction with other fine sets of questions that have other concerns. For more on this method and on Law and Gospel preaching in general, see my brief guide, Afflicting the Comfortable, Comforting the Afflicted, available from wipfandstock.com or amazon.)
1. How does the Word function in the text? This text functions first as a proclamation of God's grace in answering prayer. The people had prayed at Horeb for an alternative to the fearsome direct communication from God, and God has answered with a prophet to speak God's word. This is, then, a Gospel function, proclaiming good news. The latter verses function as Law, telling of God's judgment upon those who fail to heed the words of God's prophet, as well as on any prophet who speaks words which are not from God.
2. With whom are you identifying in the text? We are God's people, hearing this word of Law and Gospel from the mouth of Moses.
3. What, if any, call to obedience is there in this text? The call to obedience is present here as the exhortation to heed the call of God's prophet.
4. What Law/Gospel couplet is suggested by this text? Using the language from the text, we can imagine several couplets: death/life; God's fire/God's grace.
5. Exegetical work: Second century theologian, Origen of Alexandria, clearly understood that God's concern about false prophets was an example of God's care for the people. He wrote: "We can be prepared to find some prophet of impiety - and perhaps not just one but several - who will tell us of a word of the Lord, which the Lord has not at all commanded, or a 'word of wisdom' which has nothing whatever to do with wisdom. His purpose is to slay us by the word of his mouth." (Ancient Christian Commentary on Scripture, OT vol. III, p. 304). Martin Luther, in his extended Lectures on Deuteronomy, declares that this short passage is "the chief passage in this whole book and a clearly expressed prophecy of Christ as the new Teacher." (Luther's Works, vol. 9. p. 176). He goes on to say that "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." Luther continues, "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." (Ibid.). Expanding on this idea, Luther says, "...since this Prophet finds Moses teaching [the Law] 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."(Ibid., p. 178). Again, Luther says, "Since, therefore, the future Prophet is to teach differently from Moses, His Word must not be the Word of the Law, which kills and terrifies, but a Word that makes alive and consoles." (Ibid., p. 182).
6. Consider the insights of the pioneers of the New Homiletic? Henry Mitchell advised the preacher to seek the point in the text where the celebration takes place. In this text there is much to celebrate. It will be the wise preacher who raises this up.
Blessings on your proclamation!