Answer
In both modern and ancient times, a medium is a person who communicates with spirits, usually apart from the use of witchcraft. A medium is, literally, an “intermediary” between the spirit world and ours. The Bible condemns the practice of mediumship, and attempting to speak to the dead, through séances or other means, is expressly forbidden.
Sometimes mediums are called “channelers,” as they allegedly “channel” communication from the dead to the living. A medium might only communicate with one or more specific spirits (called “familiars” or “familiar spirits”), or the communication may be spread across many different spirits. The messages may come audibly, visually, or through physical sensations. Modern mediums distinguish themselves from psychics, who only read the “energies” of a person or place and do not communicate with actual spirits. (The term “psychic medium” can confuse the issue.) Also, a medium is not necessarily a witch, wizard, sorcerer, or necromancer, since mediums believe that their communication with the spirit world is an inherent ability. The fictional character Cole Sear in the movie The Sixth Sense would be considered a medium.
Mediums are referenced in several passages of the Old Testament. In Leviticus 20:27 mediums are condemned along with “spiritists.” Deuteronomy 18:10–11 echoes Leviticus and expands it, including diviners, sorcerers, witches/wizards, anyone who casts spells, and anyone who practices child sacrifice.
King Saul’s sinful use of a medium is recorded in 1 Samuel 28. The prophet Samuel was dead, and King Saul was frustrated that God had ceased telling him what to do through prophets or dreams. So the king, in direct violation of God’s Law and his own previous command, told his men to find a medium who could communicate with Samuel (1 Samuel 28:3). This medium conjured Samuel, and Saul communicated with the dead prophet. Theologians discuss whether this conjuring was a physical reappearance of Samuel or merely an image of him. There is also some question whether or not the medium actually meant to conjure Samuel, as she seems to have been the most surprised at his appearance—“When the woman saw Samuel, she cried out at the top of her voice” (verse 12). Perhaps she was a fraud who did not expect to actually see a spirit, or perhaps she was expecting to communicate with her “familiar” and not with Samuel directly. Either way, God seems to have allowed Samuel’s conjuring in order to drive home His point to Saul. The prophet’s message to Saul was one of doom (verses 17–19), and he died the next day. First Chronicles 10:13–14 reveals that Saul’s interaction with the medium was an important part of why he was dethroned and his dynasty cut short.
In the New Testament, sorcery and other associated practices are considered inappropriate, sinful activities for any Christian (Acts 8:9ff and 19:19). Since the primary purpose of these activities is to communicate with spirits, it is correct to include mediumship in these New Testament warnings.
It should be noted that the spirit a medium conjures is not the spirit of a deceased person (the case of Samuel speaking to Saul was a rare exception). Jesus’ story of the rich man and Lazarus in Luke 16:18–31 gives strong evidence that, once a person is dead, his soul remains in either heaven or hell. Thus, the spirits who communicate with mediums are lying spirits (see 1 Kings 22:23) who deceive people into believing their lost loved ones are communicating to them. When grieving parents seek out a medium to put them in touch with their dead child, they don’t realize the spirit who speaks to them is actually a demon pretending to be their child. Any involvement with such practices, including asking mediums for guidance, is strongly warned against in the Bible.
