Pascal-Emmanuel Gobry wrote a while back about the role of sacrifice in the worship of God, and says that sacrifice is all about gratitude, certainly in the New Testament, and probably in the Old Testament as well. He’s clearly on to something; the central sacrifice of the Christian faith is Christ’s sacrifice on the cross, which we participate in through the Blessed Sacrament, the Holy Eucharist; and the word “Eucharist” means “Thanksgiving”.
However, I’ve also read (I’m sorry, I cannot remember the source) that there was another purpose to the Old Testament animal sacrifices. In Egypt, the Israelites worshipped the gods of Egypt; and these, of course, were represented as men and women with the heads of animals. And at the foot of Sinai, when Moses was receiving the Ten Commandments, the people begged Aaron to make them a god; and he made them a golden calf, the figure of an animal.
When Moses commanded the Israelites to sacrifice animals to God, then, he was also commanding them to sacrifice their idols, the gods of Egypt and the golden calf: to put them to death in a colorful and memorable way, and in way that, by God’s grace, they would never return to them. The idols of Egypt were thus shown to be manifestly and entirely less than the God of Abraham, Isaac, and Jacob.
We don’t worship the gods of Egypt; but as Elizabeth Scalia has written we have in our culture a plethora—indeed, a superfluity—of idols. There are any manner of things we put before God. Some of them, like abortion, are evil on the face of it; others are entirely good—in their place. Anything we put ahead of God, whether it be sports, a political platform, our family, or even the liturgy itself, is an idol in our lives.
God calls us to sacrifice these things to Him: to repent of the ones that are sinful insofar as they are sinful, and to love all the rest according to their proper place in the order of creation; and to love Him above all. And this, too, is worship, it seems to me.
And that leads, yes, to gratitude: for what is gratitude but appreciating what God has given us in due proportion and in the proper measure?