1) The need for blood to atone for sin.
The wages of sin (what you have earned) is death.
 For the wages of sin is death; but the gift of God is eternal life through Jesus Christ our Lord.
God told Adam if he took the forbidden fruit death would be the consequence. So in order for justice to be fulfilled, it was then necessary for one to die to redeem fallen sinners.
This is depicted in the offering of the Passover lamb in the Old Testament and declared here in the new testament.
 And almost all things are by the law purged with blood; and without shedding of blood is no remission.
Jesus Christ ended all this with the giving of HIS OWN blood, once and for all time.
 For if the blood of bulls and of goats, and the ashes of an heifer sprinkling the unclean, sanctifieth to the purifying of the flesh:
 How much more shall the blood of Christ, who through the eternal Spirit offered himself without spot to God, purge your conscience from dead works to serve the living God?
 So Christ was once offered to bear the sins of many; and unto them that look for him shall he appear the second time without sin unto salvation.
Gross and revolting you say? Yes, it is. Death IS revolting. Blood gives you life, take it away and you die. Even with todays "justice", in some countries, the penalty for murder is ones own death, essentially giving your own blood as payment for your crime. Man can clean it up a bit by calling it "lethal injection" and the like. The end result is the same and just as repulsive.