1 Samuel 2:15

Before they burnt the fat. — This was a still graver offence against the ritual of the sacrifice. A contemptuous insult was here offered to the Lord. This fat was not to be eaten or taken by any one; it was God’s portion, to be burnt by the priest on the altar (Leviticus 3:16; Leviticus 7:23; Leviticus 7:25; Leviticus 7:30).

In all these strange rites and ceremonies there was a higher symbolism involved. This was ruthlessly set at nought and trampled on by these reckless, covetous guardians of the worship of Israel.
Portions of the sacrifice fell legally to the ministering priests in lieu of fee. It was fair “that they which ministered at the altar should live of the altar.” The “heave leg” and the “wave breast” of the slaughtered victim were theirs by right, and these the sacrificing priest was to receive after the fat portion of the sacrifice had been burnt upon the altar. But to take the flesh of the victim, and roast it before the symbolic offering had been made, was a crime which was equivalent to robbing God. It dishonoured the whole ceremony.

He will not have sodden flesh. — The meaning of this is, these priests and their attendants insisted on having the best part of the sacrificed victim raw, not boiled — that is, fresh, full of juice and strength — before the offering had been made.