A contradiction of Scripture
The teaching that humans have a "soul" that remains alive and conscious after they are dead, and therefore available for someone to contact, CONTRADICTS many scriptures regarding the need for a future resurrection of human life. After all, what need is there for ANY resurrection that restores consciousness back to humans if they are still conscious and alive (but in a different state of existence) AFTER they pass away?
The first resurrection of the dead is one of the chief doctrines of the New Testament Church (Hebrews 6:1 - 2). It is needed to resurrect all those who received God's Holy Spirit and remained faithful to end of their lives. Some of the many Scriptures that discuss this resurrection include Matthew 24:29 - 31, John 5:28 - 29, 1Corinthians 15:3 - 4, 12 - 14, 20, 35 - 55, 1Thessalonians 4:13 - 17, Hebrews 2:9 - 10 and Revelation 20:4, 6.
The second resurrection, by far the biggest, is needed to bring back to conscious life ALL humans who have ever lived who never received His spirit. They never received a FULL chance at understanding the Gospel, repenting of their sins and so on. Often referred to as the Great White Throne Judgment, it is discussed in Ezekiel 37:1 - 14, Matthew 25:31 - 46, Revelation 20:5, 11 - 13 and other places.
A (likely) third resurrection will be carried out to resurrect to a final punishment all those who, with full knowledge and understanding, rejected God's way and refused to repent of their sins. These people have committed what is sometimes called the unpardonable sin. Scriptures related to this judgment include Matthew 12:25 - 26, 31 - 32, Hebrews 6:4 - 8, 10:26 - 31, 2Peter 2:9 and Revelation 20:14 - 15, 21:8.
Clearly, an unconscious dead spirit awaiting a future resurrection cannot give any information to anyone!
God owns them all
Scripture teaches that God is the Being who places a spirit within each person (Zechariah 12:1) that gives them the ability to think and reason. When the flesh of a human dies, the spirit within them, which the Eternal owns (Numbers 16:22, 27:16), goes back to him.
7. And the dust return to the earth as it was, and the spirit returns to God who gave it (Ecclesiastes 12:7)
The New Testament teaches that the Almighty is the "Father of spirits" (Hebrews 12:9) and possesses the spirits of converted humans he spent the time to make perfect (verses 22 - 23).
The Bible NOWHERE teaches that the spirits of dead humans, especially those who died in the faith, are somehow available to be accessed by demonic powers. The Lord does not operate an always open spiritual "library" that allows the devil to take out any spirit and do whatever he wants with it as long as he returns it! The belief that the Eternal would allow his adversaries to "play" with human spirits (especially those he converted and worked with for many years), for their own EVIL purposes, opposes everything Scripture states he stands for!
No real world proof
The James Randi Educational Foundation, started by former stage magician James Randi in 1964, has offered a reward to anyone able to prove, under testing methods agreed to by both parties, that they have a supernatural ability like getting in touch with the dead. Since its inception, more than 1,000 folks have sought the reward, which started at $1,000 U.S. and is now at one million dollars. To date, NO ONE has been able to demonstrate such an ability!
An End Time sin
The futile attempt to contact the dead is one of the many sins committed by man during the Great Tribulation. It is one of the reasons why ONE THIRD of all humans living at that time will DIE when the sixth angel sounds his trumpet and four demons, bound by the great river Euphrates, are loosed on the earth (Revelation 9:13 - 19).
20. But the rest of the men who were not killed by these plagues still did not repent of the works of their hands, that they might not WORSHIP DEMONS, and idols of gold and silver and brass and stone and wood, which do not have the power to see, nor to hear, nor to walk. 21. And they did not repent of their murders, nor of their SORCERIES . . . (Revelation 9:20 - 21)
Conclusion of the matter
God declares that those who state they can provide the "service" of helping others contact the dead are worthy of capital punishment (Leviticus 20:6, 27, 1Samuel 28:3). He backs up his words by not allowing access to any of the spirits that have come back to him. Since the spirits of the departed are not only inaccessible to the devil, but unconscious as well, the best he and his demons can do is to deceive humans into thinking they have access to the dead.
"Mediums or sorcerers absolutely have no access to the spirits of dead people. Any manifestation belongs to evil spirits whose job is to deceive the people and bring them under the curse of God to get control over them and their offspring" (Encyclopedia of World Religions, Cults and the Occult, part four, section on seances).
The devil and his demons have NEVER been able to facilitate real communication with dead humans! Those who state they can provide a connection between the land of the living with those who have passed away are nothing more than charlatans who, at best, make money based on false pretenses or at worse provide powerful evil spirits another conduit to deceive gullible humans!