Moses sprinkled Israel with the blood of the covenant at Mount Sinai.
1 Now He said to Moses, “Come up to the Lord, you and Aaron, Nadab and Abihu, and seventy of the elders of Israel, and worship from afar. 2 Moses alone shall come near to God, but they shall not come near; nor shall the people go up with them.”
3 So Moses came and told the people all the words of God and all the ordinances, and all the people answered with one voice and said, “All the words the Lord spoke we will do.” 4 Then Moses wrote all the words of the Lord; and he rose early in the morning and built an altar at the foot of the mountain, and twelve stones according to the twelve tribes of Israel. 5 Then he sent young men of the children of Israel, who offered whole burnt offerings and sacrificed peace offerings of calves to God. 6 Moses took half the blood and put it in basins, and half the blood he poured on the altar. 7 Then he took the Book of the Covenant and read in the hearing of the people; and they said, “All the Lord said, we will do, and be obedient.” 8 Moses then took the blood, sprinkled it on the people, and said, “This is the blood of the covenant the Lord made with you according to all these words.”Exodus 24:1-8 OSB
At this point, GOD’s covenant with Israel was sealed with blood.
The blood of the covenant represented the seriousness of the deal, because life is in the blood. The symbolism was that Israel was sealing the covenant with their individual—and collective—life. And GOD was providing the substitute payment, in the life blood of the animal, in place of Israel’s own life blood.