(1) "If there arises among you a prophet or a dreamer of dreams, and he gives you a sign or a wonder, (2) and the sign or the wonder comes to pass, of which he spoke to you, saying, "Let us go after other gods"—which you have not known—"and let us serve them," (3) you shall not listen to the words of that prophet or that dreamer of dreams, for the LORD your God is testing you to know whether you love the LORD your God with all your heart and with all your soul. (4) You shall walk after the LORD your God and fear Him, and keep His commandments and obey His voice; you shall serve Him and hold fast to Him. (5) But that prophet or that dreamer of dreams shall be put to death, because he has spoken in order to turn you away from the LORD your God, who brought you out of the land of Egypt and redeemed you from the house of bondage, to entice you from the way in which the LORD your God commanded you to walk. So you shall put away the evil from your midst.
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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