Leviticus 7:13, commentary and pictures

Besides the cakes, leavened bread was to be offered with the sacrifice of thanksgiving of the peace offerings. The peace offering was especially an expression of thanksgiving to God, given in gratitude in response to the blessings He provides. The thank offering was a required offering under the Levitical system, part of the returns made to God in recognition of His claims. The thanksgiving offering was required alongside the tithe, not as a substitute for it.

In this offering the fat alone was burned on the altar, a 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 in a sacred, solemn and joyful sacrificial feast after a blessing was invoked on it. The sacrifices pointed forward to the death of Christ to preserve faith in the coming Redeemer, so the law of the offerings was to be kept strictly and solemnly. The shared feast was to direct all hearts in gratitude and faith to the great Sacrifice that would take away the sin of the world and to encourage sincere devotion, piety, kindness and sympathy rather than empty ceremony or self-indulgence.

At such a feast Elkanah gave Hannah a double portion as a sign of special regard. The sons of Eli violated this order by not being content with the part allotted to them, demanding an additional portion and claiming whatever portion pleased them. They refused to wait until the fat had been burned as an offering to God and threatened to take it by violence, using the great number of sacrifices at the annual feasts to enrich themselves at the expense of the people.