What does 1 Samuel 2:15 mean?

Even before the fat was burned for God, the priests' servants would come and demand raw meat from the person offering the sacrifice. They'd say, 'Give us meat to roast for the priest. He doesn't want boiled meat—he wants it raw.' 1 Samuel 2:15 - Modern Text Bible

(They were supposed to burn the fat as an offering to God first, but Eli's sons wanted the best parts for themselves, even before the sacrifice was finished.)