Here is Interview was done by the director of the movie. I'm Korean and I just finished watching the movie.

“<곡성>은 종구(곽도원)가 가족을 무언가로부터 2시간 36분동안 극렬히 방어하는 영화다. 종구 가족을 공격하는 건 역동적이기보단 정적이고 심리적인 무엇이다. 정적으로 잠입한 적을 어떻게 표현할까. 그건 흉기가 피부를 뚫고 뼈를 자르고 장기를 찌르는 느낌이 아니라, 바이러스가 몸에 잠입하는 것 같다고 생각했다. 바이러스는 잠입 직후엔 주목받지 못하다가 어느 순간부터 조금씩 차이를 내기 시작한다. 한국인과 유사한 외모를 가진 외국인을 찾다보니, 일본인이 적합하다고 판단했다.”

원문보기: http://news.khan.co.kr/kh_news/khan_art_view.html?art_id=201605191040001#csidx3d4b26b0831435986e45ab539532035

I'll try to loosely translate what he said. "The wailing is about a movie where the Jong Gu(The father) is trying to protect his family from an unknown super natural danger for 2 and 1/2 hours. The danger he faces does not move quickly and makes the big bang, rather it moves quietly and disturbs your scenes. How should I explain such a subtle danger? It's not like someone stabbing you with knife kind of danger. It's more like virus infection kind of danger. When you get infected with Virus, you are fine for a while but the symptoms seep in. As far as casting Japanese, I was just looking for foreign actors who resemble Koreans.

( He wanted foreinger to signify "foreign" danger. but close enough to Korean since this movie about confusion and not knowing who to trust.  )

“주인공은 심리적인 적을 극렬히 방어한다. 공성전을 생각해보자. 성문을 잠근 뒤 우군은 들여보내고 적은 막아야 한다. 대문 밖의 적을 식별할 수 없으니 의심해야 한다. 누군가는 믿고 누군가는 못믿는다. 믿음과 의심이 뒤섞인다. 이런 주제를 관통하는 은유가 있어야한다고 생각했다. 어려서부터 성경을 읽으며 자랐다. 영화의 주제를 표현하는 분명한 길을 보여주기 위해 성경을 인용했다.”

원문보기: http://news.khan.co.kr/kh_news/khan_art_view.html?art_id=201605191040001#csidxc5219304b5afdad8102e5b4bb608d01

The main character Jong gu is trying everything to defend against the unknown threat. If you think of war happening at a Castle, You need to get your team in your castle and prevent the enemy from entering the castle. but how do you know someone who wants to enter the castle is the friend or the foe? you must ponder, and have to wonder about it. You can trust some and not trust others. Your Trust(faith) or Suspicion is on a fine balance. To talk about such a topic. I needed materials to reference. I have been reading bible since I was the kid. I used the Bible verses and references to show the intention of the movie.

Basically, This movie is about a man's desperate attempt to save his family from the harm's way. but since he is fighting agaist an evil spirit, It's out of his depth to fight it by himself. He needs outside help and guidance but who do you trust? how do you know? Are they your friends or foe? Do I enter the house or not?

In the reference level.. Bible verses are used A LOT.

Matthew 4:19 New International Version (NIV) 19 “Come, follow me,” Jesus said, “and I will send you out to fish for people.”

John 8:7, viz. “He that is without sin among you, let him first cast a stone at her.”

1 Peter 5:8 New International Version (NIV) 8 Be alert and of sober mind. Your enemy the devil prowls around like a roaring lion looking for someone to devour.

Luke 24:41-43 King James Version (KJV) 41 And while they yet believed not for joy, and wondered, he said unto them, Have ye here any meat? 42 And they gave him a piece of a broiled fish, and of an honeycomb. 43 And he took it, and did eat before them.

• The girl eating the fish. ( It does not mean she is Jesus.  ) After Jesus rose, he ate a fish. it's a turning point of his being. The girl after the illness awoke up and ate fish. She is entering a different person ( possessed by evil sprit  )

Exodus 20:5 Thou shalt not bow down thyself to them, nor serve them: for I the LORD thy God am a jealous God, visiting the iniquity of the fathers upon the children unto the third and fourth generation of them that hate me;

Matthews 14:72 "72 Immediately the rooster crowed the second time.[b] Then Peter remembered the word Jesus had spoken to him: “Before the rooster crows twice[c] you will disown me three times.” And he broke down and wept."

• The good spirit warns Jong Gu to Do not enter the house. The Good spirit said I set the barrier around the house to trap the evil spirit and he just has to wait for 3 rooster crows. Jong go could not trust her, and broke in after 2.

Here is an interview given by the director of the movie. I'm Korean and I just finished watching the movie.

<곡성>은 종구(곽도원)가 가족을 무언가로부터 2시간 36분동안 극렬히 방어하는 영화다. 종구 가족을 공격하는 건 역동적이기보단 정적이고 심리적인 무엇이다. 정적으로 잠입한 적을 어떻게 표현할까. 그건 흉기가 피부를 뚫고 뼈를 자르고 장기를 찌르는 느낌이 아니라, 바이러스가 몸에 잠입하는 것 같다고 생각했다. 바이러스는 잠입 직후엔 주목받지 못하다가 어느 순간부터 조금씩 차이를 내기 시작한다. 한국인과 유사한 외모를 가진 외국인을 찾다보니, 일본인이 적합하다고 판단했다.

_Source

I'll try to loosely translate what he said:

The Wailing is about a movie where the Jong Gu (the father) is trying to protect his family from an unknown super natural danger for 2 and 1/2 hours. The danger he faces does not move quickly and makes the big bang, rather it moves quietly and disturbs your scenes. How should I explain such a subtle danger? It's not like "someone stabbing you with a knife" kind of danger. It's more like "virus infection" kind of danger. When you get infected with Virus, you are fine for a while but the symptoms seep in. As far as casting Japanese, I was just looking for foreign actors who resemble Koreans.

(He wanted foreinger to signify "foreign" danger. but close enough to Korean since this movie about confusion and not knowing who to trust.)

주인공은 심리적인 적을 극렬히 방어한다. 공성전을 생각해보자. 성문을 잠근 뒤 우군은 들여보내고 적은 막아야 한다. 대문 밖의 적을 식별할 수 없으니 의심해야 한다. 누군가는 믿고 누군가는 못믿는다. 믿음과 의심이 뒤섞인다. 이런 주제를 관통하는 은유가 있어야한다고 생각했다. 어려서부터 성경을 읽으며 자랐다. 영화의 주제를 표현하는 분명한 길을 보여주기 위해 성경을 인용했다.”

_Source

Translation:

The main character Jong Gu is trying everything to defend against the unknown threat. If you think of war happening at a Castle, You need to get your team in your castle and prevent the enemy from entering the castle. But how do you know whether someone who wants to enter the castle is the friend or the foe? You must ponder, and have to wonder about it. You can trust some and not trust others. Your Trust (faith) or Suspicion is on a fine balance. To talk about such a topic. I needed materials to reference. I have been reading the Bible since I was the kid. I used the Bible verses and references to show the intention of the movie.

Basically, this movie is about a man's desperate attempt to save his family from harm's way. But since he is fighting agaist an evil spirit, it's out of his depth to fight it by himself. He needs outside help and guidance but who do you trust? How do you know? Are they your friends or foe? Do I enter the house or not?

In the reference level... Bible verses are used A LOT.

Matthew 4:19 New International Version (NIV) 19 “Come, follow me,” Jesus said, “and I will send you out to fish for people.”

John 8:7, viz. “He that is without sin among you, let him first cast a stone at her.”

1 Peter 5:8 New International Version (NIV) 8 Be alert and of sober mind. Your enemy the devil prowls around like a roaring lion looking for someone to devour.

Luke 24:41-43 King James Version (KJV) 41 And while they yet believed not for joy, and wondered, he said unto them, Have ye here any meat? 42 And they gave him a piece of a broiled fish, and of an honeycomb. 43 And he took it, and did eat before them.

• The girl eating the fish. (It does not mean she is Jesus.) After Jesus rose, he ate a fish. it's a turning point of his being. The girl after the illness awoke up and ate fish. She is entering a different person (possessed by evil sprit)

Exodus 20:5 Thou shalt not bow down thyself to them, nor serve them: for I the LORD thy God am a jealous God, visiting the iniquity of the fathers upon the children unto the third and fourth generation of them that hate me;

Matthews 14:72 "72 Immediately the rooster crowed the second time.[b] Then Peter remembered the word Jesus had spoken to him: “Before the rooster crows twice[c] you will disown me three times.” And he broke down and wept."

• The good spirit warns Jong Gu to Do not enter the house. The Good spirit said I set the barrier around the house to trap the evil spirit and he just has to wait for 3 rooster crows. Jong Gu could not trust her, and broke in after 2.