Seeking After Familiar Spirits

Isaiah 8:16-20 

16  Bind up the testimony, seal the law among my disciples. 
17  And I will wait upon the LORD, that hideth his face from the house of Jacob, and I will look for him. 
18  Behold, I and the children whom the LORD hath given me are for signs and for wonders in Israel from the LORD of hosts, which dwelleth in mount Zion. 
19  And when they shall say unto you, Seek unto them that have familiar spirits, and unto wizards that peep, and that mutter: should not a people seek unto their God? for the living to the dead? 
20  To the law and to the testimony: if they speak not according to this word, it is because there is no light in them.