Exodus 24:8 Moses then took the blood, sprinkled it on the people and said, “This is the blood of the covenant that the Lord has made with you in accordance with all these words.”
When Moses read out all the laws he had written down from God, the people agreed to follow those rules and made sacrifices to show their commitment.
Moses took some of the blood from the sacrifices and splashed it over the people to remind them they were the ones making the commitment to God.
We cannot expect a priest or church leader to do everything so we can run off and do our own stuff; God wants faithful followers.