Charles Ellicott Commentary 1 Samuel 28:17

"And Jehovah hath done unto thee, as he spake by me: and Jehovah hath rent the kingdom out of thy hand, and given it to thy neighbor, even to David." — 1 Samuel 28:17 (ASV)

And the Lord has done to him. —Render, as in the margin of the English Version, the Lord has done or performed for Himself. The Septuagint and Vulgate here needlessly change the text into, “the Lord has done to you.”

And given it to your neighbour ... David. —An evil spirit personating Samuel would not have spoken in this way; he would not have wished to help David, “the man after God’s own heart,” to the throne of Israel; nor would an evil spirit have spoken in such solemn terms of the punishment due to rebellion against God.— Bishop Wordsworth, who argues against the supposition that the shade of Samuel was an evil spirit.