As I notice and count the gifts and joys God gives, my eyes are opened to how often giving thanks is mentioned in the Bible.
The ‘highest’ form of thanksgiving in the Old Testament is the peace offering, part of the Levitical sacrificial system. A peace offering was the only voluntary sacrifice that could be brought before God. It was also the only sacrifice in which the people were able to eat of the sacrifice. As such it was the most popular offering and is a precursor of our Christian communion meal.
No other Levitical offering permitted the inclusion of yeast as a component of the sacrifice. Yeast represents sin and contamination, so God’s inclusion of leavened bread in the thank offering shows that in giving thanks to God we are accepted even as sinful beings if we come in repentance.
In Christ we also offer our thanks on top of a prior offering for sin (see Leviticus 3:5). The price has already been paid for us, but this does not mean it cost nothing.
“And this is the law of the sacrifice of peace offerings that one may offer to the LORD. If he offers it for a thanksgiving, then he shall offer with the thanksgiving sacrifice unleavened loaves mixed with oil, unleavened wafers smeared with oil, and loaves of fine flour well mixed with oil. With the sacrifice of his peace offerings for thanksgiving he shall bring his offering with loaves of leavened bread. And from it he shall offer one loaf from each offering, as a gift to the LORD. It shall belong to the priest who throws the blood of the peace offerings. And the flesh of the sacrifice of his peace offerings for thanksgiving shall be eaten on the day of his offering. He shall not leave any of it until the morning. (Leviticus 7:11-15 ESV)