"Without the shedding of blood,
there is no forgiveness of sin." (Hb 9:22)
Sacrifice of Cain the Abel
In the Genesis 4 account we are told that God accepted Abel's sacrifice of a spotless animal but rejected Cain's offering of the first fruits of the field.
Why did God reject Cain's sacrifice?
It was not because Cain was a miser who did not offer the best of the fruits of the field, but because the penalty for sin was death and hell which required the shedding of blood. Cain made up his own way to sacrifice which was not in accordance to God's plan. Certainly, the death of an innocent animal was not equal to the death of the sinner but God, for a time, accepted the substitute (death of spotless animals) in view of the definitive sacrifice of Christ.
In Genesis 22 we read that God told Abraham, probably in a dream, to sacrifice his only son Isaac on a mountain in the land of Moriah.
Did God really command Abraham to sacrifice his only son Isaac after He had promised him many descendants?
Not likely! Further, had this been God's will, He would never have sent an angel to stop him. On the other hand, Abraham sincerely thought that God demanded this sacrifice of him since the Cananites also sacrificed their sons to the god Moloch. In spite of Abraham's error, God accepted Abraham's utter willingness to do God's will and provided for him a ram for sacrifice. This event also indicated to the Israelites that God does not desire human sacrifice. Abraham called the place Yaweh-yreh, which means, "God will see to it" or "God will provide".
The Christological dynamics present in this event are inescapable in the expression "only son" to be sacrificed and "God will provide". Indeed God sent his only Son to die for the sins of mankind. God provided the unique sacrifice.
Sacrifice of Christ
Look at Christ dying on the cross, this heart-rending sacrifice which takes away the sin of the world and cry out with David,
"Have mercy on me of God, in your goodness,
in the greatness of your compassion,
wipe away my offence" (Ps51:1)
In the Mass we sing: Lamb of God
The Christian who truly understands the profundity of his /her sinfulness and the merciful kindness of God, desires to offer the Sacrifice of Christ daily and would never think of failing to offer Christ's Sacrifice to the Father every Sunday and Holy Days.