The Dark Knight is a fantastic mimesis of the Bible.

Meaning it is very very very close to hitting the nail absolutely on the head in terms of interaction.

All civilizations are based upon a murder/scandal and doomed to failure from the start, because man is depraved. When given the choice between good and evil, left unaided, the man will choose evil the vast majority of the time.

Adam and Eve didn't exist in the garden for long.

Bruce Wayne understands this. Gotham has seen its heyday and is in decline. He is rationally a collapsaterian, he believes it will collapse and smolder, and greatness will arise from it. But he believes that doesn't have to happen. The city and the people in it are redeemable

This is basically the entire point of Batman Begins, to set this up.

"This city just showed you that it's full of people ready to believe in good."

Then we see Batman arise as a person, giving the city hope and many copycats. But, this is what makes this quote so absolutely fantastic.

“Because he's the hero Gotham deserves, but not the one it needs right now. So we'll hunt him. Because he can take it. Because he's not our hero. He's a silent guardian, a watchful protector. A dark knight.”

Bruce understands that Batman can't be what the city needs, because people can't imitate him. That's how we get copycats and this line from Bruce.

"That wasn't... exactly what I had in mind when, uh, I said I wanted to inspire people."

Thus, a person who can serve as a christ like figure, someone who is full of good and one to be imitated is required.

Enter Harvey Dent.

As soon as Harvey Dent says, "I'm the Batman" he is doomed to die. Bruce thinks Harvey is a better hero because he is someone the citizens of Gotham can imitate, much like Christ, living a perfect life is the perfect role model, Bruce understood that he was flawed as a hero.

Harvey also understood this when he prefaced his confession with, "The night is darkest just before the dawn and I promise you. The dawn is coming."

The darkness being the collective violence the city is brewing, pushing Batman to be a single victim sacrifice.

The scapegoat to "cleanse" society.

A single atonement to pay for the sins of the people.

An atonement that, when it was complete, would show them that their own evil created this and killed a man, thereby creating peace.

When Harvey's press conference convenes, everyone is without weapons. They did not come for violence. But violence occurs, because they are manipulated by the Joker.

Which brings up the joker, the most perfect comic book villain ever created, in his most perfect form in 'The Dark Knight.'

The Joker being an equivalent to Satan.

"You just couldn't let me go, could you? This is what happens when an unstoppable force meets an immovable object. You truly are incorruptible, aren't you, huh?...

...You won't kill me out of some misplaced sense of self-righteousness, and I won't kill you because you're just too much fun. I think you and I are destined to do this forever."

The Joker's entire purpose is to bring perpetual chaos, just like Satan.

"Introduce a little anarchy. Upset the established order, and everything becomes chaos. I'm an agent of chaos...”

The joker has no goal, outside of tormenting Batman.

“Do I really look like a guy with a plan? You know what I am? I'm a dog chasing cars. I wouldn't know what to do with one if I caught it! You know, I just... *do* things.”

"Some men just want to watch the world burn."
Alfred understands this. The joker wants Gotham to burn forever, feeding itself into a constant frenzy, but never dying

The Joker feeds off Batman's anger. Loving it.
-closed caption descriptor

Joker's entire being is based upon antagonizing Batman and thus the desire for this state to exist perpetually. Just as Satan wants the world to exist as is for eternity, when Christ returns and heaven and ell come to be, Satan's power is gone...

For his only power is in taking people away from God.

"Kill you? I don't wanna kill you. What would I do without you? Go back to ripping off mob dealers? No. No. No! No you- you complete me."

Which is exactly what he does with Harvey, expose him for the fallible man he is.

Harvey Dent: "You either die a hero or live long enough to see yourself become the villain"

The Joker understands this better than anyone else.

"Until their spirit breaks completely. Until they get a good look at the real Harvey Dent, huh? And all the heroic things he's done. You didn't think I'd risk losing the battle for Gotham's soul in a fist-fight with you? No, you need an ace in the hole; mine's Harvey." - Joker

"I took Gotham's White Knight and brought him down to our level. It wasn't hard. See, madness, as you know, is like gravity: all it takes is a little push."

The push is what got us the following exchange. Highlighting that Harvey is not god either, he is sinful as we all are.

Gordon: Two-Face. Harvey, Two-Face.
Harvey Dent: [turns his head, showing Gordon the mutilated side of his face] Why should I hide who I am?

But the push is also what drove the Joker and Batman to be who they are. Just as Satan is a fallen Angel, Bruce and Joker are very similar.

“Don’t talk like one of them, you’re not. Even if you’d like to be. To them, you’re a freak. Like me. They just need you know.” -Joker

Bruce is faced with confronting who he truly is at this point. The joker has poked this the entire movie,

“They need you right now, but when they don’t, they’ll cast you out, like a leper! You see, their morals, their code, it’s a bad joke. Dropped...

at the first sign of trouble. They’re only as good as the world allows them to be. I’ll show you. When the chips are down, these…these civilized people, they’ll eat each other. See, I’m not? A monster. I’m just ahead of the curve.”
-Joker

but this is the scene where Bruce is forced to understand Joker is right.

He has made himself into a savior and created a duty for himself that he cannot deny.

Harvey Dent: When their enemies were at the gates, the Romans would suspend democracy and appoint one man to protect the city, and it wasn't considered an honor it was considered a public service.

He’s just not ready for the hate that comes with it.

Alfred: Endure, Master Wayne. Take it. They'll hate you for it, but that's the point of Batman, he can be the outcast. He can make the choice that no one else can make, the right choice.

Joker on the other hand, embraces it, because he understands that Batman is indeed fallible and will not be able to completely sacrifice himself.

“The only sensible way to live in this world is without rules.”

Batman must break his only rule and kill Joker or endure this torture as long as he lives.

“The only sensible way to live in this world is without rules. And tonight, you’re gonna break your one rule”

To truly “save” the city, he must sacrifice himself, however, he knows he’s not a perfect sacrifice and thus unworthy. He does not believe his death can redeem, but is not yet ready to admit that he is irredeemable due to his one rule. Which Joker again forces him to confront.

“You have these rules, and you think they’ll save you.”

Implying that Batman’s rules would indeed not save him, forcing him to face a truly inconvenient truth. That he himself is depraved and a sinner. Batman/Bruce knows this and that is why he cannot kill Joker.

For in doing so, he would make explicit his own understanding of his own sinfulness. He would destroy the one thing he has held on to dearly. The one redeeming thing he has.

This is why he insists that Harvey’s memory not be tainted, and he take the entire blame himself. Harvey must be the Christlike figure to be imitated, the role he can never fulfill.

“Let the Joker get on with it. Gotham needs its true hero”
-Batman

There’s so much more here, but this sufficiently conveys the parallel.

This movie is brilliant. I’m just watching clips and being blown away repeatedly.

"The Joker took the best of us and tore it out”
-Gordon