Compare the marginal references.

But the prophet which shall presume to speak in my name,.... Pretending a mission and commission from God, and yet was never sent by him, like the prophets in Jeremiah 23:21,

which I have not commanded him to speak; which though true was not to be spoken in a public manner, by assuming a public office, without a divine authority or a commission from God, and much less what was false, and never commanded to be spoken at all by any:

or, that shall speak in the name of other gods; the idols of the people, as the Targum; as if any should affirm they were sent by Jove, or inspired by Apollo, as some are said to prophesy by Baal, as if they had received their orders and instructions from him, and were inspired by him, Jeremiah 2:8.

even that prophet shall die; the Targum of Jonathan is, be killed by the sword, but the Jews (q) generally interpret it of strangling.

(q) Misn. Sanhedrin, c. 10. sect. 1. Bartenora in ib sect. 5. and Jarchi in loc.

But the prophet, which shall presume to speak a word in my name, which I have not commanded him to speak, or that shall speak in the name of other gods, even that prophet shall die.

18:15-22 It is here promised concerning Christ, that there should come a Prophet, great above all the prophets; by whom God would make known himself and his will to the children of men, more fully and clearly than he had ever done before. He is the Light of the world, Joh 8:12. He is the World by whom God speaks to us, Joh 1:1; Heb 1:2. In his birth he should be one of their nation. In his resurrection he should be raised up at Jerusalem, and from thence his doctrine should go forth to all the world. Thus God, having raised up his Son Christ Jesus, sent him to bless us. He should be like unto Moses, only above him. This prophet is come, even JESUS; and is He that should come, and we are to look for no other. The view of God which he gives, will not terrify or overwhelm, but encourages us. He speaks with fatherly affection and Divine authority united. Whoever refuses to listen to Jesus Christ, shall find it is at his peril; the same that is the Prophet is to be his Judge, Joh 12:48. Woe then to those who refuse to hearken to His voice, to accept His salvation, or yield obedience to His sway! But happy they who trust in Him, and obey Him. He will lead them in the paths of safety and peace, until He brings them to the land of perfect light, purity, and happiness. Here is a caution against false prophets. It highly concerns us to have a right touchstone wherewith to try the word we hear, that we may know what that word is which the Lord has not spoken. Whatever is against the plain sense of the written word, or which gives countenance or encouragement to sin, we may be sure is not that which the Lord has spoken.