Leviticus 7:16
But if the sacrifice of his offering be a vow, or a voluntary offering, it shall be eaten the same day that he offereth his sacrifice: and on the morrow also the remainder of it shall be eaten: But if the sacrifice of his offering be a vow, or a voluntary offering, it shall be eaten the same day that he offereth his sacrifice: and on the morrow also the remainder of it shall be eaten:
The vow or voluntary offering in view was a peace offering, and especially an expression of thanksgiving to God. In this offering the fat alone was to be burned upon the altar, while a certain specified portion was reserved for the priests and the greater part was returned to the offerer to be eaten by him with his family and friends. A portion went to the priest, and the offerer distributed the remainder among the family for the shared sacred meal. That portion reserved for the people was to be eaten in a sacrificial feast on the day the sacrifice was offered, and any remainder could still be eaten on the following day, on the morrow.
The eating was a solemn but joyful feast, accompanied by prayer for God's acceptance and blessing. When rightly conducted it fostered devotion, kindness, and sympathy, rather than being mere ceremony or self-gratification. The shared meal was designed to preserve faith in the coming Redeemer and to direct all hearts in gratitude and faith to the great future Sacrifice that would take away the sin of the world. For that reason its directions had to be strictly heeded.
The sons of Eli violated this law by treating the solemn symbolic service as a means of self-indulgence. They were not content with the allotted priestly part but demanded an additional portion to enrich themselves from the many sacrifices brought at the annual feasts. They refused to wait until the fat had been burned as an offering to God, and threatened violence if denied.