Hebrews 9:18-20
Therefore not even the first covenant was inaugurated without blood. For when every commandment of the law had been declared by Moses to all the people, he took the blood of calves and goats, with water and scarlet wool and hyssop, and sprinkled both the book itself and all the people, saying, "This is the blood of the covenant that God commanded for you.

Many people get squeamish at the sight of blood. It turns our stomachs and causes some to pass out. For others, such as nurses and doctors, the sight of blood can prompt them to spring into action. But while the results might be different, the reason is similar: blood is crucial to life.

If we were to lose too much blood from our bodies, we would die. Without blood, there can be no life. And this is why blood was necessary for God's covenant: blood is the sign of life. The weight of our sin against God is so great that the only appropriate punishment is death.

When God established His covenant with Moses, the blood of goats and calves were used as a symbol of the covenant and the demand for life. It was God's mercy that allowed these sacrifices to serve as a means of atonement -- they were offered in the faith that God would one day provide a greater, more permanent sacrifice, which He did through Jesus Christ.

As he dined with his apostles at the Lord's Supper, Jesus said: "Drink of it, all of you, for this is my blood of the covenant, which is poured out for many for the forgiveness of sins. I tell you I will not drink again of this fruit of the vine until that day when I drink it new with you in my Father's kingdom." [Matthew 26:27-29]

The blood of Christ flowed from him on the cross, and it is through his blood that the new covenant with God is established and maintained.