And when the woman saw Samuel, she cried with a loud voice: and the woman spake to Saul, saying, Why hast thou deceived me? for thou art Saul.

Wesley's Notes

28:12 Saw Samuel - The words are express, the woman saw Samuel, instead of the spirit whom she expected to see, God ordering it so for his own glory. She cried with a loud voice - Terrified and astonished, and thence easily conjectured, whom she had been talking with.

Matthew Henry's Concise Commentary

28:7-19 When we go from the plain path of duty, every thing draws us further aside, and increases our perplexity and temptation. Saul desires the woman to bring one from the dead, with whom he wished to speak; this was expressly forbidden, De 18:11. All real or pretended witchcraft or conjuration, is a malicious or an ignorant attempt to gain knowledge or help from some creature, when it cannot be had from the Lord in the path of duty. While Samuel was living, we never read of Saul's going to advise with him in any difficulties; it had been well for him if he had. But now he is dead, Bring me up Samuel. Many who despise and persecute God's saints and ministers when living, would be glad to have them again, when they are gone. The whole shows that it was no human fraud or trick. Though the woman could not cause Samuel's being sent, yet Saul's inquiry might be the occasion of it. The woman's surprise and terror proved that it was an unusual and unexpected appearance. Saul had despised Samuel's solemn warnings in his lifetime, yet now that he hoped, as in defiance of God, to obtain some counsel and encouragement from him, might not God permit the soul of his departed prophet to appear to Saul, to confirm his former sentence, and denounce his doom? The expression, Thou and thy sons shall be with me, means no more than that they shall be in the eternal world. There appears much solemnity in God's permitting the soul of a departed prophet to come as a witness from heaven, to confirm the word he had spoken on earth.