Leviticus 7:18
And if any of the flesh of the sacrifice of his peace offerings be eaten at all on the third day, it shall not be accepted, neither shall it be imputed unto him that offereth it: it shall be an abomination, and the soul that eateth of it shall bear his iniquity.
Leviticus 7:11-21 gives the law of the peace offerings, which were eaten by the offerer and his friends in a sacrificial feast where the people's portion was blessed before eating. Under that division only the fat was to be burned upon the altar, a certain specified portion was reserved for the priests, and the greater part was returned to the offerer to be eaten by him and his friends. The peace offerings were especially an expression of thanksgiving to God, belonging with tithes and thank offerings among the offerings by which people showed gratitude.
They pointed forward to the death of Christ to preserve faith in the coming Redeemer in the hearts of the people and to direct all hearts in gratitude and faith to the great sacrifice that takes away the sin of the world, so the Lord's directions were to be strictly heeded in the most solemn manner. This shared worship was meant to foster true devotion, kindness, and sympathy, not to become empty ceremony or self-gratification. Under this law, peace-offering flesh eaten on the third day is not accepted, and the soul who eats it bears guilt.
The sons of Eli violated this law by failing to grasp its solemnity and turning it to self-indulgence. Discontent with their allotted part, they demanded an additional portion and used the great number of sacrifices at the annual feasts to enrich themselves at the people's expense. They refused to wait even until the fat had been burned as an offering to God, persisting in claiming whatever portion pleased them and threatening to take it by violence if denied.