Behold, the diviners and sorcerers also predict the future. What differentiates between them and a prophet?
[Though] some of the prophecies made by diviners, sorcerers, and the like materialize, some do not [as implied by Isaiah 47:13]: "Let the stargazers, the astrologers, and the diviners of what will happen in the months, come and save you from what will come upon you." [Our Sages note that the verse states] "from what" rather than "from all that."
Also, it is possible that none of their predictions will come true and they will err completely, as [Isaiah 44:25] states: "He frustrates the omens of imposters and drives diviners mad."
In contrast, all the words of a prophet come true, as [II Kings 10:10] states: "God's word will not fall to the ground." Similarly, [Jeremiah 23:28] states: "'The prophet who has a dream may relate his dream, but he who [receives] My word shall speak words of truth. What is the chaff to the grain?' declares God." This implies that the words of sorcerers and dreamers are like chaff that has been mixed with some grain, while the word of God is like grain without any chaff at all.
Concerning this, the Torah promises that a prophet will relate the truth about those matters for which the soothsayers and diviners give false- predictions to the gentiles, so that [the Jews] will not need a sorcerer, a diviner, or the like, as [Deuteronomy 18:10, 14-15] states: "Among you, there shall not be found anyone who passes his son through fire, [a sorcerer, a diviner...] For these nations... [listen to diviners and sorcerers, God has not given you this lot. God will] set up a prophet from your midst."
We see from this that a prophet will arise for the sole purpose of telling us the future events which will transpire in the world, whether there will be plenty or famine, war or peace, and the like. He even will inform a particular individual regarding his needs. Hence, when Saul lost an object, he went to the prophet to discover where it was. These are the types of things that a prophet will say. He will not come to found a new faith or add or withdraw a mitzvah.