Note the association of the word "prophet" with the phrase, "I will put my words in his mouth." This is what God told Moses He would do, so a chain of communication is set up—from God to Moses, from Moses to Aaron, and from Aaron to Pharaoh or to the people.
Contrary to what it shows in The Ten Commandments movie, the Bible suggests that Aaron did the bulk of the speaking before the people rather than Moses. This does not mean that Moses was excluded from speaking to the people, because eventually, even though it is likely that he never overcame his lack of eloquence (Exodus 4:10), he nonetheless became secure in his position as the leader. As the forty-year trial went on, he more often spoke directly to the people. When Israel finally got away from Pharaoh, Moses probably did the bulk of the speaking before the people, and Aaron faded into the background in that regard.
Every other prophet, except Christ, only built on the foundation laid in Moses. These verses particularly foretell of Christ, but it applies in principle to all the prophets that followed Moses. They all were spoken to by God, and they in turn did what Moses did: delivered the message to the ones it was addressed to.
Until New Testament times, prophets have been God's way of reaching the people. Whenever the people needed a prophet or a mediator with God, as He says in verses 16-17, God would raise up a prophet and put His words in his mouth.
John W. Ritenbaugh
Prophets and Prophecy (Part 1)
There is no doubt that God Himself is speaking. Deuteronomy 5:1-6 shows that God is speaking to Moses specifically, and through him, to the children of Israel.
More questions arise from verse 15. What does God promise to Moses and the Israelites? He promises to raise up a Prophet. Where will he come from? Note the words "a Prophet . . . from your midst, from your brethren." He will come from the tribes of Israel; the Prophet will be born an Israelite.
What special attribute will this Prophet have? The words "like me" indicate that he will be like God Himself! The Israelites are then commanded to hear the words of this Prophet. This means we are to listen and to act upon what we hear.
God shows in many places that those He appoints to the prophetic office will always preach the keeping of His commandments as evidence of the source of their guidance. They will teach the conservation of truth, that is, past truth, even as they break new ground in terms of doctrine.
Isaiah 8:19-20 is an expansion on Deuteronomy 18:15-18:
And when they say to you, "Seek those who are mediums and wizards, who whisper and mutter," should not a people seek their God? Should they seek the dead on behalf of the living? To the law and to the testimony! If they do not speak according to this word, it is because there is no light in them.
John W. Ritenbaugh
Prophets and Prophecy (Part 2)
All of us desire to know the future so we can be prepared for it. We want to be in control of our destinies and not at the mercy of events. However, some have this desire so strongly that they set themselves up as channels through which the future is revealed.
Such people have misled many. Deuteronomy 18, along with chapter 13, warns against such people. Whether they are called diviners, charmers, spiritists, or channelers, using methods like reading tea leaves, casting lots, or conducting séances, they are to be seriously and carefully avoided because there is no godly reality to their prognostications. Those seeking to know are being misguided, putting themselves at the mercy of lying demons, or at the very least, imaginative men and women.
At other times, simply following a church tradition regarding a prophecy can also mislead a person. This occurs because someone in the past, sincerely believing he understood a particular prophecy, began preaching his belief, and many in his audience then believed without the resources to prove the interpretation wrong. Due to frequent repetition, it came to be accepted as truth.
It is important for us to understand that prophets were not merely temporary and occasional expedients God would turn to. They played a vital and continuing role in Israel, especially in those times before the Word of God was widely distributed. This is why God makes provision for them within the law. He shows in many places that those He appoints to the prophetic office will always preach the keeping of the commandments of God as evidence of the Source of their inspiration. They will teach the conservation of past truths even as they break new doctrinal ground.
They both forthtell - that is, proclaim a message truthfully, clearly, and authoritatively to those for whom it is intended - and they will on occasion, but not always, foretell - that is, predict events before they take place.
It is misleading to believe these verses in Deuteronomy 18 apply only to Christ. His is undoubtedly their ultimate application, but the promise and description applies to all true, God-ordained prophets. Notice some of the identifiers in these verses:
1. God established the foundational pattern for the prophetic office in Moses ("like me").
2. God will raise a prophet up from among the Israelitish people. Later biblical sources show he might be drawn and appointed from any of the tribes and from any occupation. In other words, he did not have to be a Levite.
3. He will perform the function of a mediator between God and men (verses 16-18).
4. He will stand apart from the system already installed. He will not be antagonistic to the system, but he may be very antagonistic to the sins of those within the system, especially the leadership.
5. God will directly appoint and separate him for his office. Thus, the thrust of his service as God's representative is direct and authoritative. By contrast, the priest's function flowed from man to God by means of sacrifice - far less direct and more appealing and pleading than demanding. The New Testament ministry combines elements of both, but parallels the prophet's function more than the priest's.
Simply and broadly, a prophet is one who is given a message by another of greater authority and speaks for him to those for whom the message is intended. Thus, Moses was God's prophet, but Aaron was Moses' prophet.
Without a doubt, when we hear the word "prophet," we immediately think of the Old Testament. This is a natural reaction because that is where most of them appear in the Bible. Our memory instantaneously brings forth names like Moses, Isaiah, Jeremiah, Ezekiel, and David - all great men. However, without a doubt, the two greatest prophets of all time appear in the New Testament: John the Baptist and Jesus Christ. John the Baptist is the last and greatest under the Old Covenant, and Jesus Christ is the first and greatest of the New.
John W. Ritenbaugh
Elijah and John the Baptist