Albert Barnes Commentary Exodus 24:8

"And Moses took the blood, and sprinkled it on the people, and said, Behold the blood of the covenant, which Jehovah hath made with you concerning all these words." — Exodus 24:8 (ASV)

The blood which sealed the covenant was the blood of burnt offerings and peace offerings. The sin-offering (Leviticus 4:0) had not yet been instituted. That more complicated view of human nature which gave the sin-offering its meaning, had yet to be developed by the law, which was now only receiving its ratification. The covenant between Yahweh and His people therefore took precedence over the operation of the law, by which came the knowledge of sin (Romans 3:20).

Upon the people - Either upon the elders or those who stood foremost; or, upon the twelve pillars representing the Twelve tribes, as the first half had been cast upon the altar, which witnessed to the presence of Yahweh. The blood thus divided between the two parties to the covenant signified the sacramental union between the Lord and His people (Zechariah 9:11).