First Reading: Exodus 24:3-8
Ratifying the Covenant
3 Moses came and told the people all the words of YHWH, and all the ordinances; and all the people answered with one voice, and said, "All the words which YHWH has spoken will we do."
4 Moses wrote all the words of YHWH, and rose up early in the morning, and built an altar under the mountain, and twelve pillars for the twelve tribes of Israel. 5 He sent young men of the children of Israel, who offered burnt offerings and sacrificed peace offerings of cattle to YHWH. 6 Moses took half of the blood and put it in basins, and half of the blood he sprinkled on the altar. 7 He took the book of the covenant and read it in the hearing of the people, and they said, "All that YHWH has spoken will we do, and be obedient."
8 Moses took the blood, and sprinkled it on the people, and said, "Look, this is the blood of the covenant, which YHWH has made with you concerning all these words."
World English Bible
These verses from Exodus marked the acceptance of the covenant by the people. Actually, this was the second part of the ceremony; the first part was the meal of the 72 elders with God on the mountain top (see 24:1-2). So, a communion meal was followed by a sacrifice and sprinkling. God accepted his people (signified by the leadership meal). Then the people accepted the conditions laid down by their God (signified by the sacrifice and the sprinkling).
Sacrifice was made as a sign of self-giving to God. The blood of the animals represented life given by God. Moses used half the blood to sanctify the altars (in essence, claiming them for God). And, after the people agreed to the terms of the covenant, he threw the other half on the audience. When the people received the sprinkled blood, they acknowledged their dependence upon their Maker. Life was used to seal the bond between God and his people.
As God gave life, the people were to respond in kind. This was the underlying logic of sacrifice found in the Old Testament. To do as God does. Not as a way to usurp the Master, but to honor him.
What life have you received in prayer? At Mass? What do you give God in return?