A sin is almost always something very tiny

"One day, in the garden, he told me that a sin is almost always something very tiny, a grain of sand, a nothing—but that it can destroy an entire soul. Ah, Betty, the soul is a strong thing, an invisible, indestructible force. If a tiny pinch of sin—a nothing, a dream, a nasty thought—can destroy it, what will a large dose of poison do, a sin instilled drop by drop into the heart you want to destroy?"

I didn't really understand what he meant, but I stared at him in alarm.

—from Chronicle of the Murdered House, by Lúcio Cardoso.

I'm reading this for bookclub. I wasn't enthralled by the first few pages, but an early sudden reveal drew me in.

I am somewhat alarmed what sin may yet be revealed.