When I say this, I’m fully aware that I sound like someone who should clank when I walk and have strong opinions about chivalry. But I mean it in both a broader and more specific context.
And sin, young man, is when you treat people like things. Including yourself. That’s what sin is.
Granny Weatherwax, of Terry Pratchett’s Discworld (drawn right by Paul Kidby)

Terry Pratchett had a huge influence on me. Particularly as regards militant decency, the decision to do the right thing consistently and powered by rage. So when I speak of cowardice, I mean moral cowardice. Risk assessment resulting in avoiding physical danger and injury are actually pretty great. But moral cowardice, and deciding that the principles that you hold dear are negotiable and unimportant? That is a betrayal of self. And, to bring it back to Terry Pratchett and Granny Weatherwax, treating yourself as a thing with no moral agency.
That sounds very high-minded, doesn’t it? And also wildly impractical and irrelevant to the real world. But on the contrary: I think it’s relevant pretty often, depending what your principles are. There is a vegan in my knitting group who made their choice on animal welfare grounds. As such, it extends not just to their diet but to choices of materials – like their enthusiasm about a local yarn store now carrying blends containing Ahimsa silk.
For me, it would be downright stupid to work somewhere that campaigned against LGBTQIA+ individuals. I mean, they probably wouldn’t hire me, but part of being good at my job resulting in my life getting worse? Ridiculous. So that’s a non-issue. Where this principle becomes relevant is that I would consider it an act of cowardice to work somewhere where I was strongly encouraged (regardless of the organization’s actual mission) to never mention anything regarding LGBTQIA+ issues or felt like I could not safely bring my whole self to work. I’m not generally particularly flamboyant, but being in an environment where I wouldn’t feel comfortable making a Subaru joke would mean I was self-censoring, editing, chiseling myself down like a thing rather than a person.
Cowardice is a sin. Sacrificing portions of your self and values on the altar of palatability and lack of friction is, to me, unambiguously negative. I also think it’s unlikely to work long-term, and that the stress and misery of that is the wages of sin.
Not everyone has such clearcut priorities and principles in such easily identifiable places, but I think it is and always will be worthwhile to identify what your principles are and where they come to bear in your life.
I also don’t think being deeply and entirely convinced that cowardice is a sin is a hard and fast barrier to committing it; I am aware of my limitations and priorities. At this point in my job search I’d happily commit a few sins for a steady paycheck.
But I wouldn’t let myself pretend that they weren’t sins.