Leviticus 7:15
And the flesh of the sacrifice of his peace offerings for thanksgiving shall be eaten the same day that it is offered; he shall not leave any of it until the morning. And the flesh of the sacrifice of his peace offerings for thanksgiving shall be eaten the same day that it is offered; he shall not leave any of it until the morning.
The rule concerns the peace offering for thanksgiving, which expresses gratitude to God, requiring that its flesh be eaten on the same day it is offered with none left until the morning. The thanksgiving offering was required in addition to the tithe. It belonged to the wider system of required offerings and gifts through which Israel returned to God and was reminded that possessions came from God.
The offering was divided by rule so that the fat was burned on the altar, a specified portion was reserved for the priests, and most of it was returned to the offerer to share with family and friends in a sacrificial feast. At Shiloh this sharing was seen when Elkanah gave portions to his family and a double portion to Hannah as a sign of his regard for her. The offerer's portion was eaten as a sacred, solemn yet joyful feast after being set apart and blessed with prayer for God's acceptance and blessing.
When rightly conducted, the feast fostered devotion, kindness, and sympathy rather than mere ceremony or self-gratification. The offerings and their prescribed handling pointed forward to Christ's death and were meant to turn hearts in gratitude and faith toward the great Sacrifice who would take away sin, so disregard for their sacred order dishonored God and obscured their meaning.