Around Tokyo
What is the Matter in this World and an Afterlife
The battle against Satan is one of the main themes of the Gospels. It was confirmed by Johann Christoph Blumhardt (1805 – 1880), a German Lutheran theologian, when he healed a girl in two-year-long demonic possession.It was said that the demonic manifestation ended one night with the demon shouting "Jesus is the victor". Blumhardt was considered by some as a hero on the basis of the incident, but he insisted that Christ was the hero, quoted as saying: "That I don´t know, but this I do know; Jesus is the victor". (https://en.wikipedia.org/wiki/Johann_Blumhardt)
This incident was then, namely around 1850, thought to have proved that power of Christ Jesus was still alive and effective after 1800 years since the crucifixion of Christ Jesus. Although exorcism is sometimes performed today mainly by Catholic bishops, this exorcism by Blumhardt gave strong influence on Karl Barth (1886 – 1968), a Swiss Reformed theologian who is most well known for his involvement in the Confessing Church, and authorship of the Barmen Declaration, a document adopted by Christians in Nazi Germany who opposed the Deutsche Christen (German Christian movement). (https://en.wikipedia.org/wiki/Karl_Barth; https://en.wikipedia.org/wiki/Barmen_Declaration).
In the era of modernism when people came to neglect spiritual power while heavily relying on modern science and technology, Blumhardt stressed that spiritual power of Christ Jesus was still alive and effective through the exorcism activity. For example, the late John-Paul II is said to have performed exorcism three times by himself, although he seems to have failed in the third time before his death in 2005.
Although spiritualism, seances, etc. became popular in the Victorian era, involving Conan Doyle (1859 – 1930), Blumhardt's case is the most reliable about spiritual phenomena.
What is at issue is that fight against Satan has been continuing in these 2000 years. For example, WWI, WWII, tragedies in Auschwitz, etc. were caused by Satan. So, WWIII would surely occur in this trend, since even today people and churches have not focused on Satan and demons as their enemies.
What's more, Satan and demons are also spiritual entities. Therefore, this battle against Satan must continue even after men die and go into the spirit world till they are accepted in Heaven. So, spiritual mediums and those with supernatural powers might be under control of Satan, demons, or evil spirits. Only sincere Christians like Blumhardt could be trusted.
Incidentally, Blumhardt also gave influence on a unique Japanese writer (1925-2000) whose father was a Christian priest. He wrote some unique books such as "Amen-Father" depicting his father who was a sincere but half-crazy (according to his son) priest following his passion toward Christ Jesus.
Existence of spirits of dead men in the spirit world is the secondary matter. The focus should be fight against Satan. How one fights against Satan in this world while living in this world and in the spirit world while living in the spirit world or an afterworld is the matter.
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Luke 6, King James Version
13 And when it was day, he called unto him his disciples: and of them he chose twelve, whom also he named apostles;
14 Simon, (whom he also named Peter,) and Andrew his brother, James and John, Philip and Bartholomew,
15 Matthew and Thomas, James the son of Alphaeus, and Simon called Zelotes,
16 And Judas the brother of James, and Judas Iscariot, which also was the traitor.
17 And he came down with them, and stood in the plain, and the company of his disciples, and a great multitude of people out of all Judaea and Jerusalem, and from the sea coast of Tyre and Sidon, which came to hear him, and to be healed of their diseases;
18 And they that were vexed with unclean spirits: and they were healed.