Jamieson, Fausset and Brown on 1 Samuel 28:3

3. Now Samuel is dead, &c.--This event is here alluded to as affording an explanation of the secret and improper methods by which Saul sought information and direction in the present crisis of his affairs. Overwhelmed in perplexity and fear, he yet found the common and legitimate channels of communication with Heaven shut against him. And so, under the impulse of that dark, distempered, superstitious spirit which had overmastered him, he resolved, in desperation, to seek the aid of one of those fortune telling impostors whom, in accordance with the divine command (Le 19:31; 20:6, 27; De 18:11), he had set himself formerly to exterminate from his kingdom.