Sin is real?

an excerpt from an article about Discworld

when Granny brings all that power to bear on the world, it’s in the defense of a simple, humble view of what goodness and evil are. In Carpe Jugulum, she winds up arguing about right and wrong with a novice preacher, who is fearful of making absolute statements — committed to seeing all the shades of gray. Granny rebukes him:
“There’s no grays, only white that’s got grubby. I’m surprised you don’t know that. And sin, young man, is when you treat people as things. Including yourself. That’s what sin is.”
“Oh, I’m sure there are worse crimes—”
“But they starts with thinking about people as things …”
Reading that as an atheist, it was the first time I’d seen a definition of sin that didn’t sound like, as Francis Spufford describes our modern use of the word in Unapologetic, a kind of “enjoyable naughtiness” that seemed mostly to do with sex or very expensive chocolates...

But the kind of sin that Granny talks about isn’t an indulgence in something harmless, luxurious and secret. And it’s not the world-shaking evil of a monster or a murderer. It’s a seemingly small rejection of creation and the particular place our fellow people have in it. It’s not always choosing hatred; it can be putting aside love for indifference.But it’s an insidious sort of error that harms me along with the person I’m rejecting. They’ll be hurt by the way I treat them, but I’m wounded by my self-inflicted blindness. I’ve robbed myself of the chance to see the other person as God does, and to love them in his way.,,,
Instead, the work that is left to Granny, and to all of us, more closely resembles St. Therese of Lisieux’s advice to “miss no single opportunity of making some small sacrifice, here by a smiling look, there by a kindly word, always doing the smallest right and doing it all for love.” In the moment, Pratchett’s heroes are a little more curmudgeonly than Therese, but they keep doing the next right thing: refusing to discard others or see them as things.