Leviticus 7:19
And the flesh that toucheth any unclean thing shall not be eaten; it shall be burnt with fire: and as for the flesh, all that be clean shall eat thereof. And the flesh that toucheth any unclean thing shall not be eaten; it shall be burnt with fire: and as for the flesh, all that be clean shall eat thereof.
This law belongs to the peace offerings, which were especially an expression of thanksgiving to God. Flesh that has touched anything unclean must not be eaten but must be burned with fire, while clean flesh may be eaten. In these offerings only the fat was burned upon the altar, a specified portion was reserved for the priests, and the greater part was returned to the offerer to be eaten by him and his friends in a sacrificial feast, with the people's portion blessed before it was shared.
The sacrifices pointed forward to the death of Christ and were designed to preserve faith in the coming Redeemer, so the Lord's directions concerning them were to be strictly heeded. Thus all hearts were to be directed in gratitude and faith to the great Sacrifice that was to take away the sin of the world. When rightly observed, the shared feast was sacred and was meant to encourage true devotion, kindness, and sympathy rather than mere ceremony or self-gratification.
The sons of Eli violated this law by not being content with the part allotted them, demanding an additional portion, refusing 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. In a further application, the verse is also connected with trespass offerings that people return to God as an expression of gratitude for His blessings.