ISAIAH REPEATEDLY condemned the practice of summoning spirits from the netherworld. 

It’s not always apparent because translators often didn’t have an understanding of the cult of the dead that surrounded ancient Israel, and the impact it had on the Israelites. After prophesying the imminent destruction of the northern kingdom of Israel by Assyria, the prophet condemned the people of Judah for turning to mediums and necromancers to ”inquire of the dead on behalf of the living”. 

Derek wrote about Isaiah 8:18–22 in The Second Coming of Saturn: 

The prophet described those who looked to the spirit realm for oracles as people who were already dead: They live in darkness, and they’re “greatly distressed and hungry,” like the pagan dead of Mesopotamia who are not properly cared for by their descendants. In verse 21, Isaiah makes the connection to the dead explicit, writing that these unhappy souls will “pass through” the land. The Hebrew verb ‘ābar is based on the same root, ʿbr, from which we get ʿōberim—“Travelers,” as in the spirits of the dead who “travel” or “cross over” from the land of the dead to the world of the living; it’s the same word used by the pagan Canaanites to describe the Rephaim summoned from the underworld through rituals to the threshing-floor of El on Mount Hermon. 

What Isaiah described is the punishment for those who defied God by using ritual pits to summon the spirits of the dead—they become like the unhappy dead themselves. When they realize their fate, “they will be enraged.” But in the context of the passage, with an understanding of the cult of the dead and the role of the “king” god in it, a better translation of the following sentence is this: “And they shall curse by Molek and by their ghosts.” (Elohay, the word translated “ghosts,” isn’t always a reference to God. The basic meaning is “one who lives in the spirit realm.” Context is king, and here “ghosts” or “spirits” is a more accurate reading than “God.”) 

-- The Second Coming of Saturn, p. 188.