Romans12chapter 12

"Present your bodies as a living sacrifice" borrows from the one religious practice everybody in the empire understood. Temples ran on animal sacrifice — the smoke, the meat, the fees. Paul asks for the same act with the worshiper himself on the altar, alive, which is why he calls it a reasonable or spiritual service.

The body-with-many-members image was a familiar political metaphor in Rome. A famous old fable had the parts of the body quarrelling with the stomach until they learned they needed each other, and Roman speakers used it to tell the lower orders to accept their place. Paul takes the same picture and uses it to level rather than to rank: each member belongs to all the others.

The instructions that follow describe life in cramped shared housing — practicing hospitality, weeping with those who weep, not being proud, associating with the lowly, feeding an enemy. In a culture organized by honour, patrons, and reciprocal favours, refusing to repay evil and declining to seek revenge were social oddities.

The line about heaping burning coals on an enemy's head comes from Proverbs and is best read as the shame that kindness produces, not as a hidden way of hurting him.