Jamieson, Fausset and Brown on Isaiah 8:19

19. Seek unto--Consult in your national difficulties.

them ... familiar spirits--necromancers, spirit charmers. So Saul, when he had forsaken God (1Sa 28:7, &c.), consulted the witch of En-dor in his difficulties. These follow in the wake of idolatry, which prevailed under Ahaz (2Ki 16:3, 4, 10). He copied the soothsaying as he did the idolatrous "altar" of Damascus (compare Le 20:6, which forbids it, Is 19:3).

wizards--men claiming supernatural knowledge; from the old English, "to wit," that is, know.

peep--rather "chirp faintly," as young birds do; this sound was generally ascribed to departed spirits; by ventriloquism the soothsayers caused a low sound to proceed as from a grave, or dead person. Hence the Septuagint renders the Hebrew for "necromancers" here "ventriloquists" (compare Is 29:4).

mutter--moan.

should not, &c.--The answer which Isaiah recommends to be given to those advising to have recourse to necromancers.

for the living, &c.--"should one, for the safety of the living, seek unto (consult) the dead?" [Gesenius]. Lowth renders it, "In place of (consulting) the living, should one consult the dead?"