Isaiah now gives counsel to the faithful. He notes that there will be some who turn to worldly prognosticators. He is referencing a practice in the ancient world of those who communed with the spiritual realm in unusual sounds and unintelligible utterances. Isaiah declares that they should listen to the prophets of the living God rather than those who pretend to commune with the dead for information.
A way to discern among those who would prophesy is to compare them to the law and to the testimony. Isaiah uses those two terms to indicate all of the scriptures. If a proposed prophet does not accord with the scriptures, “it is because there is no light in them.”
Those false prophets will not be fed by the scriptures, but remain hungry. They reject Jehovah, and when they look to the heavens, they do not see light, but rather darkness.