Fridge Brilliance: Initially the fact the doors were the only way to defeat Crain comes off as a perfect example of Fridge Logic and poor writing—why would Crain include in his own house the very thing that would defeat him, and before he ever became a malevolent ghost, no less? But if you take into account Crain's Holier Than Thou attitude from the novel (and his book of morality for his daughters), the doors make sense as yet another example of his fixation upon being one of the Moral Guardians with a stern belief in a Fire and Brimstone Hell. What he didn't count on, then, was that God would work through those very doors to end his reign of terror and mete out proper punishment.
Fridge Horror: Read a little deeper into the supernatural side of the movie. Crain didn't play with the kids when they were alive - he killed them in the house when they were young, and kept building rooms for them, and having statues and carvings made of them. All so they would be there even after his death. The house is a giantSoul Jar.