"Others warm by the fire at the center of the monastery"

"warm", in that context is being used as a verb, as in "Come inside and warm yourself." or "Let's warm the chicken in the microwave."

or as in

My grandma and your grandma
Sitting by the fire
My grandma says to your grandma
"I'm gonna set your flag on fire"

BTW, I second the need to ($_='warm').='ing' as hinted elsewhere in this thread.