Adam Clarke on Deuteronomy 13:1

If there arise among you a prophet - Any pretending to have a Divine influence, so as to be able perfectly to direct others in the way of salvation; or a dreamer of dreams - one who pretends that some deity has spoken to him in the night-season; and giveth thee a sign, אות oth, what appears to be a miraculous proof of his mission; or a wonder, מופת mopheth, some type or representation of what he wishes to bring you over to: as some have pretended to have received a consecrated image from heaven; hence the origin of the Palladium, Numa's Shields, and many of the deities among the Hindoos. But here the word seems to mean some portentous sign, such as an eclipse, which he who knew when it would take place might predict to the people who knew nothing of the matter, and thereby accredit his pretensions.