The word familiar is from the Latin familiaris, meaning a “household servant,” and expresses the idea that certain sorcerers possessed spirits as their servants ready to obey their commands. Those attempting to contact the dead, even to this day, usually have some sort of spirit guide who communicates with them. These are familiar spirits.
“Do not turn to mediums or wizards; do not seek them out, to be defiled by them.” –Leviticus 19:31
“There shall not be found among you any one who burns his son or his daughter as an offering, any one who practices divination, a soothsayer, or an augur, or a sorcerer, or a charmer, or a medium, or a wizard, or a necromancer. For whoever does these things is an abomination to The Lord; and because of these abominable practices The Lord your God is driving them out before you. You shall be blameless before The Lord your God.” –Deuteronomy 18:10-13
The medium was one who acted as a “go-between” to supposedly contact or communicate with the dead, but in reality they were contacting demons who convinced the mediums that they were “familiar” and could be trusted and believed. The practices associated with mediums and familiar spirits were banned in Israel, and the punishment for practicing such things was death.
The Old Testament Hebrew word for those with familiar spirits meant a bottle, since they were regarded as a vessel for the inspiring demon. The New Testament Greek word was equivalent in meaning, and whether they were fakers, or actually possessed by a spirit, the people of God were to have absolutely nothing to do with them.
To this day, familiar spirits (demons) are under the control of their master, Satan. They influence people to spread lies and deceit in order to thwart the kingdom of God. Knowingly opening oneself to the work of demons is an evil thing.
Some avenues through which demons, a.k.a. “familiar spirits,” can gain entrance into a person’s life are divination, transcendental meditation, visualization, necromancy, witchcraft, drugs, and alcohol. These are all activities that believers are exhorted, commanded even, to avoid. Instead, we are to be filled with the Holy Spirit, with love, with joy, and with the fullness of life that comes from Jesus Christ. We are also to be on guard, “for our struggle is not against flesh and blood, but against the rulers, against the authorities, against the powers of this dark world and against the spiritual forces of evil in the heavenly realms” — Ephesians 6:12.