Many of you have seen the film The Exorcism of Emily Rose. The film scared the jeepers out of me and I only finished it because it had some pretty heavy theological implications.
The most disturbing element of the film is that Emily Rose is depicted as a redeemed Catholic Christian in a state of grace who is asked by God and the Blessed Virgin Mary to suffer demonic possession so that the rest of the world will come to appreciate the supernatural. Emily Rose is said to be possessed by six demons, one of which is Lucifer himself:
The first one, (In Hebrew)- "Anee-hoo-sheshokhen-betokh-CAIN."("I am the one who dwelt within CAIN!")
The second one, (In Latin)- "Ego sum unus quisnam habito intus Nero."(I am the one who dwelt within NERO!")
The third one, ( In Ancient Greek)- "Eh-no-ente-so-paro-thene-JUDAS-een."(I once dwelt within JUDAS!")
The fourth one, ( In German)- "Eet-ik- nik- LEGION."(And I was with LEGION!")
The fifth one, (In Assyrian Neo-Aramaic)- "Ah-nah-BELIAL!"( I am BELIAL!")
The sixth one, (In English)- "And I am Lucifer, the devil in the flesh!"The film is based on the true story of Anneliese Michel, a young German Catholic woman who died in 1976. I don't know if the story of the six demons belongs to the original story of Anneliese.
A Catholic Perspective
St. Paul and St. Thomas Aquinas teach the redeemed soul in a state of grace is not only infused with grace but by this grace is also indwelt by the Holy Spirit. This is not metaphorical. God dwells in the human soul by grace and resides there as if enthroned in a hallowed temple.
How then can the soul of Anneliese Michel be indwelt by both God and Satan at the same time? God says, "I shall not share by glory with another" (Is 42:8). How then could God share a soul with Satan?
In a similar situation, St. Paul explains that he had been given over to be tormented by an evil spirit:
 And to keep me from being too elated by the abundance of revelations, a thorn was given me in the flesh, a messenger of Satan, to harass me, to keep me from being too elated.The concept is similar. A demon is introduced and by virtuous patience, God's glory is manifested. It is clear that St. Paul grants that God allows evil spirits to "harass" us. This also occurred to Job (cf. Job 1) However, the case of Job and Paul are not cases of demonic possession. The problem with the Emily Rose film or the true story of Anneliese Michel is that it depicts a person in a state of grace possessed by a demon (or many of them). Again we come back to the question, how can God and Satan dwell in the same soul?
 Three times I besought the Lord about this, that it should leave me;
 but he said to me, "My grace is sufficient for you, for my power is made perfect in weakness." I will all the more gladly boast of my weaknesses, that the power of Christ may rest upon me. (2 Corinthians 12)
St. Thomas Aquinas writes: "And yet the Holy Ghost is possessed by man, and dwells within him, in the very gift itself of sanctifying grace. Hence the Holy Ghost Himself is given and sent." (Summa Theologiae I. 43. 3)
Perhaps one way to solve the riddle is to say that the soul of Anneliese Michel was indwelt by the Holy Spirit, but her body was possessed by devils. This would be the only way to get around the obvious contradiction. However, St. Paul says this of the indwelling of the Holy Spirit:
Do you not know that your body is a temple of the Holy Spirit within you, which you have from God? (1 Cor 6:19)For St. Paul, the indwelling of the Holy Spirit in the soul is the same as the indwelling of the Holy Spirit in the body. I don't think that St. Paul's understanding of the human person allows for the strict bifurcation of the human soul from the body (while it is still living). Thus, it seems that Anneliese was in a state of grace and not possessed by devils; or she was possessed by devils and not in a state of grace.
If anyone has any other ideas, please contribute. I think this is a very interesting topic and regardless of our theologizing, let us be charitable and take a moment to pray for the soul of Anneliese Michel.