Albert Barnes Commentary 1 Samuel 28:6

"And when Saul inquired of Jehovah, Jehovah answered him not, neither by dreams, nor by Urim, nor by prophets." — 1 Samuel 28:6 (ASV)

When Saul inquired of the Lord... It is said in 1 Chronicles 10:14 that one reason the Lord killed Saul and gave his kingdom to David was because he did not inquire of the Lord.

This apparent discrepancy is explained by the fact that inquiring of a familiar spirit was fundamentally opposed to inquiring of the Lord.

That Saul received no answer when he “inquired of the Lord”—whether by dreams (a direct revelation to himself), by Urim (an answer through the high priest wearing the ephod), or by prophets (an answer from a seer speaking the Word of the Lord, as in 1 Samuel 22:5)—should have been a reason for self-abasement and self-examination. He should have sought to find and, if possible, remove the cause of God's silence. This, however, was no justification whatsoever for his sin in asking counsel from a familiar spirit.