1. The prophet Samuel had died, probably about five years before, when David was hiding in the wilderness from Saul. The king could not have seen the real Samuel in the flesh, as it was well after the prophet's death.
2. Sometime before, Saul had gone to great lengths to rid Israel of mediums and spiritists. Apparently, his agents had not done a thorough job, but his decree had driven those practices underground, and their practitioners feared the punishment of violating the law—death (I Samuel 28:9).
More than anything, these details provide insight into Saul's state of mind.
