The first factor added here is that God recognizes that false prophets, through the power of Satan, can accomplish signs and wonders. The magicians of Egypt imitate Moses' staff-into-a-serpent miracle before Pharaoh (Exodus 7:8-12). The end-time False Prophet will do similar signs as the Two Witnesses, causing most of the world's population to worship the Beast (Revelation 13:11-15). Paul warns in II Corinthians 11:13-15 that Satan's servants are clever counterfeits of Christ's. Signs, wonders, and miracles, then, are not conclusive proof that a prophet is from God.
The second factor Deuteronomy 13 adds is our need to recognize the spiritual message accompanying the prophet's signs and predictions. This is the essence of the apostle John's admonition, "Beloved, do not believe every spirit, but test the spirits, whether they are of God; because many false prophets have gone out into the world" (I John 4:1). No matter how impressive or accurate a prophet's miracles or prophecies, his credibility hangs on whether he leads people toward or away from God.
The following questions, then, must all be answered before we judge a person as a true or false prophet:
1. Does he claim to prophesy in God's name or in a false god's name?
2. Do his prophecies come to pass?
3. Does he do signs and wonders?
4. Does he teach the truth based on God's Word?
Richard T. Ritenbaugh
Was Herbert Armstrong a False Prophet?
This passage begins with the assumption that the prophet does foretell the future accurately or perform some other, humanly impossible work. Nevertheless, if that prophet's central message is to follow after a different god or to take a spiritual path that the true God has not said to take, that person is a false prophet. God states unequivocally that misrepresenting Him incurs the death penalty, and Revelation 19:20 says that this is exactly what happens to the False Prophet: He is thrown into the Lake of Fire.
The message of the false prophet is contrasted in Deuteronomy 13:3-4 with loving the true God with all of our heart and soul (life), walking after Him, fearing Him, keeping His commandments, obeying His voice, serving Him, and holding fast to Him. These elements indicate what God wants His people to be focused on, helping to define whether a man claiming to speak for God is truly doing so or not.
Verse 4 mentions obeying God's voice and keeping His commandments. This is a regular theme with God's true prophets: They always have God's law undergirding their messages. When the Old Testament prophets were sent to warn or inform Israel and Judah, they always pointed out the grievous ways in which the people had transgressed God's law.
False prophets, on the other hand, will not hold the moral line that God requires. Lamentations 2:14 says that the false prophets "have not uncovered your iniquity, to bring back your captives, but have envisioned for you false prophecies and delusions." False prophets will not connect the dots between the sinfulness of a nation and national calamity. They instead focus on something other than God's standard of righteousness.
This same principle appears in Isaiah 8:19-20. Both houses of Israel were guilty of seeking out mediums and wizards for spiritual guidance, and God's response is very telling:
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.
God gives us a standard by which to measure the words of a prophet: the law and testimony - His Word. If the prophet's message contradicts what is already established as God's Word, it is evidence that he lacks spiritual understanding. If his words do not line up with God's law and testimony, he is not speaking the truth.
In summary, the hallmark of a true prophet is his upholding of the law of God, while false prophets dodge moral teaching and instead preach a message that appeals to the masses. God's truth - and His law in particular - is abhorrent to the natural mind (Romans 8:7), and thus it is quite common for God's prophets to be killed, while the false prophets enjoy widespread popularity and support.
The current trend of outcome-based churches serves as a good example. Their leaders preach a widely popular message, and thousands of people follow them. Yet, Jesus says in Luke 6:26, "Woe to you when all men speak well of you, for so did their fathers to the false prophets." Popularity is not a good measurement of God's pleasure with a leader!
Jesus Christ, the most perfect Spokesman for God who has ever lived, only had about 120 true followers when His ministry ended (Acts 1:15). This was not due to failure on His part, but because His Father's message could be wholeheartedly believed only by those whose minds God had already prepared to accept it.
"Purpose-Driven" church leaders will not preach the unadulterated Word of God because they know it is divisive. It would also thwart their goals of a large following and a large income. Thus, their messages do not involve repentance, sound doctrine, or God's law, except where it may serve to further whatever purpose is driving them. Their messages do not remind people of their moral responsibilities to God and brother, and thus if they claim to speak for God or say that God sent them, we can know from biblical patterns that they are, in fact, false prophets. Their large churches, as amazing as they might seem, are not accurate indicators of God's involvement or blessing.
David C. Grabbe
What Is a False Prophet?
In each case, Christ's admonition is that we should have a healthy skepticism of miracles because miracles may produce deception. It is not that the miracle does not occur. The more important point is, does it witness to the truth? Does it witness to the ultimate reality, the will of God?
In both Jesus' instruction in the New Testament (Matthew 24:24; 7:22-23; Revelation 13:13-14) and in Moses' teaching in the Old Testament (Deuteronomy 13:1-5), it is clear—regardless of the wonder done—if a person even implies that we are free to disobey God, the miracle is not a demonstration of God's truth. A miracle it was, but it does not validate God's truth.
We must be especially skeptical of those who say that they believe in keeping God's laws, and then turn right around and say that the Sabbath and holy days are no longer necessary and that "true Christians" can keep Christmas, Easter, Halloween, etc. But they "believe" that they are to keep God's laws! It is especially deceptive because so many of such people are really nice individuals.
John W. Ritenbaugh
Is God a Magician?
This is the earliest formal warning to God's people that attacks against their faith would take place within the fellowship of His children, and the pattern has occurred repeatedly. God raises up a prophet or minister to instruct His people. Opposition arises, usually in the form of ministers who see things differently, who force the people to choose which way they will follow. Understand, God is not passively watching. He actively tests His children's loyalties through such calamitous situations.
John W. Ritenbaugh
God's Sovereignty and the Church's Condition (Part Two)
What is coming from the prophet's mouth? Something false. Who is this prophet speaking for, what supernatural spirit? It is not the spirit of God, but a demon speaking through a human being, inspiring and motivating him. God permits it and expects His people to put that person to the test. God expects us to be able to discern the spirit that is motivating the speaker. The test is to see whether we will remain loyal to God—loyal in terms of keeping His commandments.
Thus, the listener better have a good working knowledge of God, which returns us to II Corinthians 10:5, where Paul warns that reasonings will exalt themselves against the knowledge of God. This clarifies the devices that Satan will use to turn us aside. This also underlines our need to be able to thwart those devices. We need to have a good working knowledge of God—not things about God so much, but the knowledge of God the Person, the Being with whom we have a relationship.
Also, Deuteronomy 13 confirms that some of these false prophets will be able to do miracles, which Paul confirms in II Thessalonians 2, and John confirms in Revelation 11. What is in the New Testament is built upon what God has already shown in the Old Testament—that Satan's modus operandi will be carried through from one covenant to the other. We have to understand that such signs—the ability to do miracles—are not of themselves indications of authority from God. They must be combined with teaching that agrees with God's already revealed will.
John W. Ritenbaugh
Satan (Part 2)
It is a prophetic voice that speaks for God, and His prophets will always have as the basis of their prophecy the commandments of God as evidence. The message they give (predictive or not) will always be in harmony with previously revealed truth, even though the prophet may be breaking new doctrinal ground, which happens now and then.
We can see another difference between a prophet and a priest or minister. The priest or minister conserves old truth and implements new truth given by the prophet. Most of the time new truth will come through a prophet. Under the New Covenant, of course, new truth came through apostles who were about as close to prophets as one can get without being prophets. Paul makes that clear when he lists the offices in the church, listing apostles first and prophets second (Ephesians 4:11). Once we leave the Old Covenant for the New, God uses apostles to announce new truth, and the prophet is moved into a secondary position. However, throughout the Old Testament, new truth or new doctrines came through prophets.
A minister's job is to conserve what has already been given, to hold fast to what was given in the past, and to recognize that new truth comes through an apostle. There is no apostle now, so we should not expect that there will be any new truth. However, if God raises up a prophet, then we also have to recognize that new truth can come through him. He will not break God's pattern. New truth will either come through an apostle or a prophet. The prophet breaks new ground, yet he also conserves the old.
There is a difference between a minister and a prophet. A minister does not give new truth but conserves old truth. The prophet or the apostle will conserve the old and also proclaim the new.
John W. Ritenbaugh
Prophets and Prophecy (Part 1)