Then he shall kill the bull before the LORD, and Aaron's sons the priests shall bring the blood and throw the blood against the sides of the altar that is at the entrance of the tent of meeting.
The book of Leviticus records various laws and traditions for the people of Israel to obey. The most important of these involve how man relates to God: how he is to approach God and how he is to deal with his sin in order to face a holy God for whom sin is utterly offensive.
The blood of sacrifice is the means shown by God for man to become clean. Seemingly disgusting statements like "washed in the blood of the lamb" are actually symbolic of the true sacrifice which satisfies justice, and allows us to enter into eternity with God.
That true sacrifice was the shed blood of Jesus, dying on the cross to take punishment for sin for those who believe in him to do so. All Old Testament sacrifice contains a representation and promise of the Saviour to come.