I just saw the movie and was very confused but then I read <PERSON>'s comments and did some thinking (<PERSON>'s comments were like my cliff notes.)
My thoughts:
1 - This was a movie with a Christian flair that has a few Biblical references (the stone casting by the young mysterious lady, the 3 rooster calling at the end of the film.) And there was a scene where the policeman met with a Christian priest and the priest told him that he cannot help if he continues to use a Shaman to solve the problem.
2 - The Shaman was always with the devil. In the Christian faith, all types of super natural act are considered acts of the devil (miracles performed by <PERSON> notwithstanding.) Witch doctors, shamans, fortune tellers are frowned upon by Christianity. The fact that he vomited in the presence of the young mysterious lady was a sign that he was the evil in the presence of God. The moth attack on his car was not the act of the devil but the act of God. And as <PERSON> pointed out, he wore the same undergarment as the possessed Japanese man - a subtle hint by the filmmaker.
3 - The young mysterious lady was a God like figure. She was always following the Japanese man.
4 - Again as <PERSON> pointed out, the rituals that the <PERSON> and the Japanese man were doing were not related. The goal was to confuse us a little bit using some of the traditional supernatural rituals that are often used in more generic asian horror movies pitting the good against the evil to create an exciting "fight" scene. I think the point was the <PERSON> was doing his thing to generally try to convince people to believe in his supernatural powers - i.e. Convincing people to believe in a false god. The ritual performed by the japanese man was actually to fight off God trying to cast the devil out of him which succeeded. The mysterious lady <PERSON> figure showed up right after it was done.
5 - The zombie was the dead man that got possessed by the devil after it was cast out of the Japanese man by the mysterious lady. 829
Then after the zombie got incapacitated, it re-possessed the Japanese man.
6 - The movie had a theme of faith or lack of (at least it's one of the themes.). Here is an average joe that really couldn't do anything right. He appeared a bit male chauvinistic and lacked any kind of conviction. At the end of the movie, he simply didn't have enough faith and got his family killed (I don't blame him though since it would've been hard on anyone to make a decision either way.) And also at the end of the movie when the devil revealed himself in his true form in the cave, he said to the priest aid - if you already believe I'm the devil, then I'm already the devil. Reverse that, if you don't believe there is God, then there is no God. I think the point here was the devil didn't need to reveal himself for us to believe in his existence (the priest aid already "knew" he was the devil) but we often expect God to reveal himself before we believe in him (as the policeman didn't trust the mysterious lady at the end.). Bad things happen and we think they're the devil's acts. When good things happen, we often attribute them to our own doing.
Just my humble conclusions. I was too confused while watching the movie to appreciate it. But I think it has a lot of subtleties and undertones that are usually missing in more mainstream horror movies. I wish it was scarier since I also like simple, straightforward good scares. 133