made no sense

I wholeheartedly disagree! What fun would that be? :)

the main story of The Wailing was actually about Good
(the woman in white/angel) vs Evil (the japanese guy/ the devil). The Village/villagers was/were the battlefield/pawns. The Japanese guy was the devil worshipper at the beginning (he plagued the village with his dark activities) but his body was possessed by the devil after he died. so the shaman continued the jap's works (he went back to the village after the devil gave him a sign by raining him with dirts/bird's poo or something. I forgot)in the end, the devil won the game. the villagers believed more in ghost/supernatural stuff but not in God.

And this is exactly my issue with the movie. Nobody truly knows what the hell transpired but everyone calls it "deep and thought provoking". Not saying it's a bad movie (although it's most definitely not my cuppa tea) but my personal preference is that even if a movie is open-ended, there needs to be a fair amount of clues littered throughout to be able to piece the puzzle together in a coherent manner.

This one just threw everything up in the air, layered it with some impressive imagery but then left it almost exclusively to the audience members to theorize the meaning. That doesn't work for me.

agreed...very frustrating to watch...

I'm all for a cerebral horror but there's a line between great storytelling (ie, The Usual Suspects) and pretentiousness. I'm afraid this film falls into the latter category. Just unnecessarily convoluted.

I think this explanation is the most correct one!

Sequence of events:

Under influence of evil Tengu, Monk rapes and infects Police daughter.
Police destroys Monk's ritual room, kills his dog and threatens to kill him if he does not leave in 3 days.
In response, Monk hangs dead goat to curse police family further (father paralyse momentarily, daughter went rabid and kills neighbour). He also proceeds to prepare a ritual to revieve zombie to protect himself/kill villagers.
A good/famous Shaman was brought in by police's mother.
Shaman removed Tengu's hidden crow curse and performs a high risk out-of-body hex to kill Monk. For a successful ritual, Shaman warns police there should be no interruption / visiter / drinking etc.
Although the hex is directed at the Demon, the daughter being under the control of the Demon, also suffers in pain and pleads for her father to stop the hex.
Monk almost died from the Shaman's hex but wakens when the police interrupted the ritual. The hex backfires, giving opportunity for Demon to leave the Monk and control Shaman instead.
Monk (now good) returns to his room to recuperate. Youko sees that he is no longer possessed, hence did not hurt him even though he is weakened.
Good Monk awakes and remembers that the zombie is revieved and may hurt people. He panicks and hurries to find it.
Fearing for his daughter's life, the Police went with his friends to the Monk's house to kill him.
Planning to make the villagers sin and lessen the village's protection from Grandma or Youko, the Demon contols the zombie to lure Monk back to his house to be killed by villagers.
Monk tries to escape the angry villagers but fell down a short cliff. He cries at the thought of his past sins and at the irony of his circumstance as his original intent was to save the villagers.
Monk sees Youko and chases after her. Being a fox spirit possessing a young woman, perhaps she fears of being captured/exocised by the good Monk, or she is accquinted with the Monk in the past and does not wish to reunite with him.
While chasing, Monk slips down clift and knocked against police's lorry.
Police and gang throws Monk over road's cliff.
Shaman (now bad) laughs as the Deman's plan to make the villagers sinners was successful, and that the Demon was able to fully take over the body of the dead/critically injured Monk.
Shaman returns to the Police house to collect the souls. However, Youko overpowers him.
Fearing for his life, he abandons his mission and flees home. The Crow Demon reminds Shaman that he has to work for him by blowing off the lited candle (no buddha can protect him) and sending a dead crow (death omen).
Shaman tries to flee the village, but the Demon sends moths to further instil fear in Shaman for the consequences in abandoning his task.
Shaman returns back to village (as seen on the road signage "Gokseong") and resumes his task by tricking the police that the young woman is the demon instead of the Monk.
As the policeman has sinned, the Youko and Grandma can no longer prevent the demon's complete take over of the daughter, nor the deaths of his family. However, Youko tries to trap the Demon and prevent the Shaman from collecting their souls. The trap will be successful if the police does not step past the flower trap after the rooster crows 3 times.
Unfortunately, the police's faith wavered when he saw Youko with the infected human being's belongings (including his daughter's hairpin), and he returned home to find that his daughter has murdered the whole family.
Shaman then came to take photo/collect souls.

THRILLER IS MY FOOD!

I've read many theories about this film, but I like that it does leave it all open to interpretation.

I think this could be a battle for souls, and neither entity is necessarily good. There's a possibility that the Japanese man wasn't the devil, as he taunts the priest by both showing stigmata, and a devilish appearance, but he also points out to the priest that it is what he is expecting to see - it is a test of faith. The girl taunts Jong-Goo by not giving him straight answers either, but tests his faith too by asking that he wait for the rooster to crow 3 times. Both fail the test: Jong-Goo loses his family and his sanity, and the priest gets his picture taken - presumably to be one of the next victims.

More evidence: Both the woman and the Japanese man are incredibly sinister. They both collect something from the victims. The Japanese man is at least more human in the beginning - he has a house, a dog, a passport. She is more ghost-like, disappearing at will, giving cryptic messages. Both have some sort of Christian traits: she throws stones, he is resurrected.

I think that she is the original evil, and the Japanese man was encroaching on her turf. I also think it is her resurrecting the dead. Jong-Yoo's family die before the third rooster crow but maybe her despair is that the souls belong to the Japanese man, and not her. Between the two of them they are using the villagers to battle off (remember she says she has set a 'trap' for the old man) as well as using their lack of faith and ridiculous superstition into play to drive them crazier and crazier.

As for the city slicker shaman, he too is being manipulated by both. I don't think he works for one or the other, and the reason he can't get his divinations right is because both are evil, rather than just one being good. In this case his own arrogance is his downfall, even though he's the one that gets to walk away with the end, clearing up the evidence of his own failings as he flees the scene.