Deuteronomy 13:8

The first case. If a prophet, or one who had dreams, should rise up to summon to the worship of other gods, with signs and wonders which came to pass, the Israelites were not to hearken to his words, but to put him to death. The introduction of חלום חלם, "a dreamer of dreams," along with the prophet, answers the two media of divine revelation, the vision and the dream, by which, according to Num 12:6, God made known His will. With regard to the signs and wonders (mopheth, see at Exo 4:21) with which such a prophet might seek to accredit his higher mission, it is taken for granted that they come to pass (בּוא); yet for all that, the Israelites were to give no heed to such a prophet, to walk after other gods. It follows from this, that the person had not been sent by God, but as a false prophet, and that the signs and wonders which he gave were not wonders effected by God, but σημεῖα καὶ τέρατα ψεύδους ("lying sings and wonders," Th2 2:9); i.e., not merely seeming miracles, but miracles wrought in the power of the wicked one, Satan, the possibility and reality of which even Christ attests (Mat 24:24). - The word לאמר, saying, is dependent upon the principal verb of the sentence: "if a prophet rise up...saying, We will go after other gods."

Moses is still upon that necessary subject concerning the peril of idolatry. In the close of the foregoing chapter he had cautioned them against the peril that might arise from their predecessors the Canaanites. In this chapter he cautions them against the rise of idolatry from among themselves; they must take heed lest any should draw them to idolatry, 1. By the pretence of prophecy (Deu 13:1-5). II. By the pretence of friendship and relation (Deu 13:6-11). III. By the pretence of numbers (Deu 13:12-18). But in all these cases the temptation must be resolutely resisted and the tempters punished and cut off.