Leviticus 7:12
If he offer it for a thanksgiving, then he shall offer with the sacrifice of thanksgiving unleavened cakes mingled with oil, and unleavened wafers anointed with oil, and cakes mingled with oil, of fine flour, fried. If he offer it for a thanksgiving, then he shall offer with the sacrifice of thanksgiving unleavened cakes mingled with oil, and unleavened wafers anointed with oil, and cakes mingled with oil, of fine flour, fried.
The instruction concerns the peace offering when brought as thanksgiving, which is especially an expression of gratitude to God. The thanksgiving sacrifice was to be brought with specified cakes and wafers prepared with oil. Only the fat was to be burned on the altar, while a specified portion was reserved for the priests and the greater part was returned to the offerer. That returned portion was to be shared with family and friends in a solemn but joyful sacred feast, with a blessing asked upon it before eating and the remainder distributed among the family.
The law was corrupted by Eli's sons, who were not content with the allotted priestly portion but demanded an additional portion, refused to wait until the fat had been burned to God, claimed whatever portion pleased them with threats of violence, and used the great number of sacrifices at the annual feasts to enrich themselves at the people's expense. Like the other sacrifices, it pointed forward to the death of Christ to preserve faith in the coming Redeemer and to direct all hearts in gratitude and faith to the great Sacrifice that would take away the sin of the world, so its directions were to be strictly heeded. Thanksgiving offerings were required in addition to the tithe, or tenth of increase, as part of a system of required returns that made many claims on property, proportioned to what each possessed, to support religious service and benefit the poor. Through such offerings people return a portion to God in gratitude for His blessings, including health and the ability to acquire means. This shared worship was meant to encourage true devotion, piety, kindness, and sympathy, not to become empty ceremony or self-gratification.