Throughout scripture one constant theme is that wherever there is a covenant, there must be a sacrifice; and wherever there is a sacrifice, there must be the shedding of blood. This agrees with the description of Gods people as
"those who cut My covenant on the basis of a sacrifice." Psalm 50:5
Two things are essential for entering into a permanent relation with God: a covenant and a sacrifice.
WITHOUT A COVENANT THERE CAN BE NO RELATIONSHIP WITH GOD.
WITHOUT A SACRIFICE, THERE CAN BE NO COVENANT.
Before the Cross, man entered into covenant with God through ceremony. This was during a period in Israels history when the nation was backslidden and rebellious in their relationship to God, and they had done something God forbade them to do. They had made slaves out of their fellow Israelites. When God rebuked them for this through the prophet Jeremiah, they made a show of repentance and entered into a covenant in which they agreed to release their slaves. But then, to add to their sin, they broke their covenant and took the slaves back.
"And I will give the men who have transgressed My covenant, who have not fulfilled the words of the covenant which they made before Me, when they cut the calf in two and passed between its parts - the officials of Judah, and the officials of Jerusalem, the court offices, and the priests, and all the people of the land, who passed between the parts of the calf and I will give them into the hand of their enemies." Jeremiah 34:18-2
For this treacherous dealing with God they are severely threatened.
"Be not deceived; God is not mocked."