In I Samuel 28, King Saul visits the witch of Endor and asks her to call up Samuel from the dead. "Samuel" then tells Saul that he and his sons will soon die, for God has rejected him from being king.
Was that really Samuel? My Armstrongite background answers "no." For Armstrongites, the dead are unconscious, for Ecclesiastes 9:5 says that the dead do not know anything, and Psalm 6:5 states that the dead in Sheol do not give thanks to God. This doctrine is known as "soul sleep." Armstrongites maintain that what Saul saw couldn't have been Samuel, but a demon.
The identity of "Samuel" in I Samuel 28 has been debated throughout the history of biblical interpretation. From what I can see, Jewish interpretations seemed to maintain that Samuel was the one who appeared to Saul. Jesus ben Sira (second century B.C.E.) says in Sirach 46:20 that Samuel prophesied even after his death, and Josephus (first century C.E.) affirms in Antiquities 6:332ff. that the soul of Samuel came up from Hades. The rabbis also think it was Samuel (see here).
Within Christianity, however, there was much more disagreement. I was reading the Ancient Christian Commentary on Scripture last night, and I saw that Justin Martyr believed it was Samuel, whereas Tertullian thought it was a demon. Origen tries to refute those who claim it's a demon. From Keil-Delitzsch's commentary, I learned that Martin Luther and John Calvin voted "demon."
Soul sleep isn't always the reason that Christians vote "demon." Eighteenth century Calvinist commentator John Gill and others say that Samuel couldn't come from the ground, since his soul was in heaven with God. So you can tell that soul sleep is not a factor in their conclusion!
Perhaps the biggest issue in the "demon" explanation is this: the Torah condemns seeking familiar spirits (Exodus 22:18; Leviticus 19:31; Deuteronomy 18:9–14), so certain Christians don't think that God would have honored necromancy by allowing a witch to bring up Samuel from the dead.
But what about the message of "Samuel"? He spoke God's word, didn't he? He said that Saul and his sons would die, and that God was rejecting him from being king. Would a demon speak the truth?
Those who claim that this was a demon have various answers for that. Some say that a demon can speak the truth, or that God can use a demon to accomplish God's will (I Kings 22:23). Others contend, however, that the demon was not conveying God's message. According to Matthew Henry and Ellen White, God would have encouraged Saul to repent rather than discouraging him and kicking him when he was down, as "Samuel" does in I Samuel 28. As many Christians today assert, the Holy Spirit convicts, whereas Satan condemns, and that's one way you can tell the difference between the two.
What's my position? I think it was Samuel for the reasons that the Nelson Study Bible enumerates: "It seems best to follow the early view that this was a genuine appearance of Samuel which God Himself brought about. Several points favor this interpretation: (1) The medium was surprised (v. 12); (2) Saul identified the figure as Samuel (v. 14); (3) the message Samuel spoke was clearly from God (vv. 16–19); (4) the text says that the figure was Samuel (vv. 12, 15, 16)." In my opinion, God was at work here, so Samuel did not arrive through the machinations of the necromancer. That's why she was so surprised!
One more point: I don't really see a conflict between I Samuel 28 and biblical passages asserting that the dead don't know anything. I Samuel 28:15 says that Saul "disturbed" Samuel. P. Kyle McCarter states: "The verb rendered disturbed here refers specifically to the interruption of the rest of the dead (cf. 'Sheol beneath is stirred up' in Isa 14:9); it occurs in ancient tomb inscriptions as a description of the activity of graverobbers." Ordinarily, the dead are resting, but someone or something can arouse them out of their sleep. We may see something like that in Isaiah 14, in which the kings in Sheol are aroused and taunt the king of Babylon. Maybe the Old Testament view on the afterlife is that the dead usually were ignorant and unconscious because they were resting, but they could become conscious when someone woke them up!