Albert Barnes Commentary 1 Samuel 15:23

"For rebellion is as the sin of witchcraft, and stubbornness is as idolatry and teraphim. Because thou hast rejected the word of Jehovah, he hath also rejected thee from being king." — 1 Samuel 15:23 (ASV)

The meaning is that rebellion is as bad as the sin of divination, and stubbornness is as bad as worshipping false gods (iniquity) and teraphim (idolatry).