Albert Barnes Commentary Leviticus 19:31

"Turn ye not unto them that have familiar spirits, nor unto the wizards; seek them not out, to be defiled by them: I am Jehovah your God." — Leviticus 19:31 (ASV)

The devotion of faith, which manifests itself in obedience to the commandment to keep God’s Sabbaths and to reverence His sanctuary (Leviticus 19:30), is the true preservative against the superstition forbidden in this verse. The people whose God was Yahweh were not to indulge those wayward feelings of their human nature which are gratified in magical arts and pretensions. .

Familiar spirits—literally, “bottles.” This application of the word is thought to have been suggested by the tricks of ventriloquists, within whose bodies (as vessels or bottles) it was imagined that spirits spoke. In other cases, the word is used for the familiar spirit that a man pretended to employ to consult, or to raise, the spirits of the dead. (See 1 Samuel 28:7–8).

Wizard—a word equivalent to “a knowing man” or “a cunning man”.