22 Moses said to the people, "This is the blood of the covenant God has established with you." Practically everything in a will hinges on a death. That's why blood, the evidence of death, is used so much in our tradition, especially regarding forgiveness of sins.
Matthew Henry's Commentary on Hebrews 9:22
Commentary on Hebrews 9:15-22
(Read Hebrews 9:15-22)
The solemn transactions between God and man, are sometimes called a covenant, here a testament, which is a willing deed of a person, bestowing legacies on such persons as are described, and it only takes effect upon his death. Thus Christ died, not only to obtain the blessings of salvation for us, but to give power to the disposal of them. All, by sin, were become guilty before God, had forfeited every thing that is good; but God, willing to show the greatness of his mercy, proclaimed a covenant of grace. Nothing could be clean to a sinner, not even his religious duties; except as his guilt was done away by the death of a sacrifice, of value sufficient for that end, and unless he continually depended upon it. May we ascribe all real good works to the same all-procuring cause, and offer our spiritual sacrifices as sprinkled with Christ's blood, and so purified from their defilement.