On demons, angels, Heaven and Hell... there are a lot of popular and wrong theology about these things.
Unfortunately, a lot of even otherwise good Christians fail to believe God on these matters.
What is important about these matters is people need to understand that evil spirits are not to be feared nor should people assume they know all on spiritual matters. Answers never come by saying, "I know, I know".
Very often I see Christians not able to take authority against wicked powers in prayer because they have learned wrong things about the spiritual world.
For instance, note the verse below, which is pretty much universally accepted as speaking of the Devil:
Isaiah 14
12 How you have fallen from heaven,
O morning star, son of the dawn!
You have been cast down to the earth,
you who once laid low the nations!
13 You said in your heart,
"I will ascend to heaven;
I will raise my throne
above the stars of God;
I will sit enthroned on the mount of assembly,
on the utmost heights of the sacred mountain. [
c]
14 I will ascend above the tops of the clouds;
I will make myself like the Most High."
15 But you are brought down to the grave,
to the depths of the pit.
16 Those who see you stare at you,
they ponder your fate:
"Is this the man who shook the earth
and made kingdoms tremble,
17 the man who made the world a desert,
who overthrew its cities
and would not let his captives go home?"
Note how he is described as "a man".
Ezekiel 28 also speaks of the condemnation of the Devil, and is as well, universally accepted as doing so... and also shows how he is but a man.
It even speaks of him being killed:
9 Will you then say, "I am a god,"
in the presence of those who kill you?
You will be but a man, not a god,
in the hands of those who slay you.
10 You will die the death of the uncircumcised
at the hands of foreigners.
I have spoken, declares the Sovereign LORD.' "
11 The word of the LORD came to me: 12 "Son of man, take up a lament concerning the king of Tyre and say to him: 'This is what the Sovereign LORD says:
" 'You were the model of perfection,
full of wisdom and perfect in beauty.
13 You were in Eden,
the garden of God;
every precious stone adorned you:
ruby, topaz and emerald,
chrysolite, onyx and jasper,
sapphire, [
b] turquoise and beryl. [
c]
Your settings and mountings [
d] were made of gold;
on the day you were created they were prepared.
(If then the leader of the wicked spirits is shown to be as just a man in his end, then what of all the lesser spirits of destruction.)
Likewise, there are many such verses. For instance, Revelation 12 speaks of the Devil and 'one third of the stars of Heaven' being 'thrown down to earth'.
Further, we know from several books in the Bible angels did choose to leave their places and when they did so they became as men. And they died.
In popular Jewish literature demons were considered to be a select number of the ghosts of these ones who were doomed to wander the earth for a period of time.
Not much is spoke of such things outside of symbolic language, though Paul does mention that the saints 'will judge even the angels'. Now, consider this: will that judgment happen at the millennium, or afterwards. And either way, is it not so that we 'do not swear by the Great City for that is the City of the King'? And where is that great city, but on earth.
As we are asked to pray: "Your Kingdom come on earth as it is in Heaven".
People also fail to understand Heaven. If Heaven is in the bosom of Abraham, as Jesus said, then what of Jesus? And how is it a man was able to see someone 'in the heart of Abraham' even though he was in punishment, in Hell? (Heaven is in the heart of Abraham, but the real "father of nations" is Jesus Christ.)
Also, to show how little people know about these things, consider the Lord's words on the coming of the Kingdom of God:
Luke 17
20Once, having been asked by the Pharisees when the kingdom of God would come, Jesus replied, "The kingdom of God does not come with your careful observation, 21nor will people say, 'Here it is,' or 'There it is,' because the kingdom of God is within[b] you." 22Then he said to his disciples, "The time is coming when you will long to see one of the days of the Son of Man, but you will not see it. 23Men will tell you, 'There he is!' or 'Here he is!' Do not go running off after them. 24For the Son of Man in his day[
c] will be like the lightning, which flashes and lights up the sky from one end to the other. 25But first he must suffer many things and be rejected by this generation.
26"Just as it was in the days of Noah, so also will it be in the days of the Son of Man. 27People were eating, drinking, marrying and being given in marriage up to the day Noah entered the ark. Then the flood came and destroyed them all.
None of this is strange: for God himself came as man in the form of Jesus Christ. What then of angels?
Further, angels are described as children of God. If they are then strange beasts, how then are we also called children of God? Are we of different substance and nature, or is there more then one God?
But the Spirit of Jesus within our hearts is the Spirit of God and the wicked spirits are but as spirits of mere men of the earth: therefore, people should not be afraid to take authority over any wicked spirit.
As for 'talking to the dead', that is obvious condemned in Scripture as necromancy, though Jesus spoke to Elijah and Moses: neither were "dead" or He would not have done it.
As for Samuel being brought up from the grave through a medium:
1 Samuel 28
8 So Saul disguised himself, putting on other clothes, and at night he and two men went to the woman. "Consult a spirit for me," he said, "and bring up for me the one I name." 9 But the woman said to him, "Surely you know what Saul has done. He has cut off the mediums and spiritists from the land. Why have you set a trap for my life to bring about my death?"
10 Saul swore to her by the LORD, "As surely as the LORD lives, you will not be punished for this."
11 Then the woman asked, "Whom shall I bring up for you?"
"Bring up Samuel," he said.
12 When the woman saw Samuel, she cried out at the top of her voice and said to Saul, "Why have you deceived me? You are Saul!"
13 The king said to her, "Don't be afraid. What do you see?"
The woman said, "I see a spirit [
a] coming up out of the ground."
14 "What does he look like?" he asked.
"An old man wearing a robe is coming up," she said.
Then Saul knew it was Samuel, and he bowed down and prostrated himself with his face to the ground.
Notice Samuel is seen 'as coming up from the ground'.
I mentioned all of these verses on this thread, it is easy enough for people to look them up if they are ignorant of them.
It is important for people to believe what is Scripturally correct if they wish to speak on such matters, and not just what they have heard from scholars or popular opinion.
All we can do as Christians, however, is tell the truth: not all believe us. Obviously, however, it is much harder to believe on matters of Heaven then it is on matters of earth, so this does not mean someone is not a Christian just because they embrace foolish notions of spiritual powers.