Necromancy is a sin.
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Leviticus 20:5-8 Then I will set my face against that man and against his clan and will cut them off from among their people, him and all who follow him in whoring after Molech. “If a person turns to mediums and necromancers, whoring after them, I will set my face against that person and will cut him off from among his people. Consecrate yourselves, therefore, and be holy, for I am the LORD your God. Keep my statutes and do them; I am the LORD who sanctifies you.
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Leviticus 19:31 Turn not unto necromancers and unto soothsayers; seek not after them to make yourselves unclean: I am Jehovah your God.