As others have mentioned a sacrifice was performed to reconcile with God. In the old covenant the sacrifices of Able and Abraham were pleasing to God. After eating of the fruit of the tree of knowledge Adam and Eve were cast out of Eden. Once no longer in the garden, mankind lost access to the tree of life as well, and as a result of original sin mankind knew death.
The sacrifices of Able and more importantly Abraham were steps to restoring the covenant relationship with God. When delivering his people from Egypt, God sent a series of plagues to persuade Pharoh. The 10th plague was the death of the first born sons. So that this plague would pass over the Hebrews, God instructed Moses to have the people sacrifice an unblemished male of 1 year age from either the sheep or the goats. The people must place the blood of the sacrifice upon the lintel and door post of their homes, and each family was required to eat the flesh of the sacrifice and to burn what could not be eaten. In doing this the angel of death would pass over their household.
The blood holds life, hence the kosher prohibition on consuming blood. The Jews in the temple continued to offer sacrifices of unblemished male lambs for the expiation of sin. However, these sacrifices were not sufficient to truly forgive sin and the sacrifices had to be offered continually because they could not blot out our sinfulness.
In his mercy, God sent his only son who was without sin as a perfect sacrifice for the whole world. Jesus is the Lamb of God, the perfect unblemished lamb that is sacrificed. This perfect sacrifice would be sufficient to expiate all sin. In the Mass the bread and the wine are consecrated seperately – when the blood is seperated from the body we are participating in the very same sacrifice of the passion. At the last supper Jesus breaks the bread before giving it to his deciples – hence the body of the Christ must be broken before we can eat. At Mass we eat his flesh, flesh of the perfect Lamb of God, in the transfigured bread as the Hebrews ate the flesh of the passover lamb. At Mass we drink his most precious blood so that the angle of death will pass over us, as the Hebrews painted the blood of the passover lamb upon the doorway to their homes. While nailed bloody to the wood of His Cross, the Christ’s body became for us the fruit on a new tree of life.
God in His mercy condescended to die for us that we might be redeemed and the revelations of salvation history would be fufilled. “Oh who am I, that for my sake, my Lord should take frail flesh and die?”
