If you’ve ever spent time on a farm, maybe you got to watch the farmer, as he took the carcass of a dead animal he found in the paddock, and threw it on a fire to get rid of it. You watched over the next hour or so, as the carcass was slowly transformed into bones and ashes.
You don’t realize it as first, but that’s the kind of image Paul picks up on here in these verses. He’s drawing on the Old Testament sacrifices, and the pagan sacrifices that the Romans would have been more familiar with. They had stood by, as the sacrifice they had brought was burnt before their eyes, slowly transformed into dust and ashes.
Here, though, it’s us that are urged to offer ourselves as sacrifices; with the way to do that, and the outcome, rather different to the OT and pagan sacrifices.