What They Are Not
They are not the spirits of the dead communicating messages to the living.
In one of the earliest written portions of Holy Scripture, the Lord declared plainly that the dead have no knowledge of the living:
"He passeth: Thou changest his countenance, and sendest him away. His sons come to honor, and he knoweth it not; and they are brought low, but he perceiveth it not of them." Job 14:20, 21.
The dead have no part in any communications with the living on earth:
"Neither have they any more a portion forever in anything that is done under the sun." Eccl. 9:6