nor diminish from it
Deuteronomy 12:32
12:32 nor diminish from it. See also Deuteronomy 4:2; Proverbs 30:6; Matthew 5:18; Revelation 22:18,19. The Word of God is eternally settled in heaven (Psalm 119:89), and it is dangerous presumption for men and women to try to dilute or augment it.
13:3 Thou shalt not hearken. Even if a “prophet” or magician is allowed by God to make a true prediction or perform a genuine miracle, that is not sufficient proof of his authenticity as a man of God. He must also be using his ability to glorify the true God and confirm His word, not to undermine His authority and lead people into a false religion. “To the law and to the testimony: if they speak not according to this word, it is because there is no light in them” (Isaiah 8:20). This warning is as relevant today as it was in ancient Israel, especially in view of the wide resurgence of occultism, pantheism, and all kinds of paranormal phenomena–all opposing true Biblical Christianity.