Nothing too nasty could happen in such a nice little town. Not there. (2.150)
This is doubly ironic. First, something nasty is totally going to happen. And second, that nastiness happens because the town isn't nice at all, what with all the adultery and meanness and, you know, Satanic rituals (in Marsten's day at least).
"O my father, favor me now. Lord of Flies, favor me now. Now I bring you spoiled meat and reeking flesh. I have made sacrifice for your favor. With my left hand I bring it. Make a sign for me on this ground, consecrated in your name. I wait for a sign to begin your work." (3.431)
This sounds like an ancient evil ritual, but it's really just some spooky stuff King made up. The Lord of Flies is Satan, of course, so the suggestion is that Barlow and Straker are minions of the devil.
He wanted to see EVIL with its cerements of deception cast aside, with every feature of its visage clear. He wanted to slug it out toe to toe with EVIL… He wanted the struggle to be pure, unhindered by the politics that rode the back of every social issue like a deformed Siamese twin… Heaven was a dim attraction compared to that of fighting—and perhaps perishing—in the service of the Lord. (6.299)
This is Father Callahan, wishing for serious Evil to fight, rather than all the little evils like poverty and lust and Mrs. McDougall beating her baby. This wish to be a hero battling evil seems like pride, and therefore it's kind of evil, too—though it's not exactly clear if the novel sees it that way. (After all, the novel thinks fighting big Evil is fun too.)
And in the awful heavy silence of the house, as he sat impotently on his bed with his face in his hands, he heard the high, sweet, evil laugh of a child—
—and then the sucking sounds. (7.215)
Danny Glick slipping through the window is pretty much the embodiment of evil. He's innocence totally corrupted.
"The devil, according to the Gospel According to Freud, would be a gigantic composite id, the subconscious of us all."
"Surely a more stupendous concept than red-tailed boogies or demons with such sensitive noses that they can be banished with one good fart from a constipated churchman," Matt said.
"Stupendous, of course. But impersonal. Merciless. Untouchable. Banishing Freud's devil is as impossible as Shylock's bargain—to extract a pound of flesh without spilling a drop of blood. The Catholic Church has been forced to reinterpret its whole approach to evil… It is in the process of shedding its old medicine-man skin and re-emerging as a socially active, socially conscious body…."
Matt said deliberately, "and you hate it don't you?" (13.82-13.87)
Callahan wants the big Evil to fight, in part because those little evils are so tricky. Freud, the father of psychoanalysis, thinks evil is inside everyone, Callahan says, and so you can't really fight it. In part the vampires refute that: they're clearly evil, through and through. In part, though, they seem to confirm Freud, since the vampires can be seen as just the evil of the townspeople made manifest.
"In the name of God the Father!" he cried, and his voice took on a hoarse, commanding note that made them all draw closer to him. I command the evil to be gone from this house! Spirits, depart!"…
There was a flash of light… The new Yale lock lay on the boards at their feet, welded into an almost unrecognizable mess…
Callahan withdrew from the door, trembling. He looked down at the cross in his hand. "This is, without a doubt, the most amazing thing that's ever happened to me in my life," he said. (14.243-244)
Faced with the unholy Marsten House, Callahan calls down the power of goodness (or of the White, as Barlow puts it). What that power is, exactly, is somewhat unclear. Is it God? The specifically Catholic God? Or what? Does blowing off the Yale lock mean that the Church is the one true church, and a force for goodness? Or is the Church just a kind of superpower? (See "Symbols: The Cross" for more.)
"But I have lived longer than you. I am crafty. I am not the serpent, but the father of serpents.
In the end, 'Father' Callahan, you will undo yourself. Your faith in the White is weak and soft. Your talk of love is presumption. Only when you speak of the bottle are you informed." (14.278)
Here's where Barlow burbles about the White and faith. Again, what he means by it is unclear: is the White supposed to be God? Or is it just a chess metaphor? Anyway, he's right about Callahan, who does in fact undo himself. 'Salem's Lot is iffy on what Callahan needs to have faith in, but it's clear that his lack of faith isn't good.
"Nowhere left to go," Barlow murmured sadly. His dark eyes bubbled with infernal mirth. "Sad to see a man's faith fail. Ah well…" (14.514)
And here's where Callahan's cross sputters out and Barlow gets him. The infernal mirth here has to be King's as well as Barlow's—this is one of the novel's most enjoyably perverse scenes. You wouldn't want to do without this passage, which means that on some level, you're probably rooting for Barlow to get Callahan and have him drink that vampire blood. As in lots of horror, the monsters are often more enjoyable than the good guys. Go evil!
"It's better this way," Mark said. "My father… he would have made a very successful vampire. Maybe as good as Barlow, in time. He… he was good at everything he tried. Maybe too good." (14.853)
Barlow just up and kills Mark's dad, so Mark's dad doesn't get to be a vampire. Mark, though, seems to assume that when people turn into vampires, they keep their selves in some sense: if you were efficient and smart as a human, you'll be efficient and smart as a vampire. It seems like vampiredom is just as aspect of humanity. Evil isn't a weakness, in this view; it's just using your strengths to another purpose.
"He'll make a good vampire, though, once he gets the hang of it."
Mark was looking at him with rising horror, and Ben knew he had to get him away. This was the worst of all. (14.1097-1098)
Parkins thinks Nolly will make a good vampire not because he's smart (like Mr. Petrie), but because he's kind of dumb and mean-spirited. Parkins's refusal to be a vampire, his conviction that he wouldn't like being a vampire, in some ways makes him more evil himself ("the worst of all"). Being indifferent and damning your neighbor—that's also kind of evil, right?