Why Blood

Hebrews 9:15-18 (CSB)
[15] Therefore, he is the mediator of a new covenant, so that those who are called might receive the promise of the eternal inheritance, because a death has taken place for redemption from the transgressions committed under the first covenant. [16] Where a will exists, the death of the one who made it must be established. [17] For a will is valid only when people die, since it is never in effect while the one who made it is living. [18] That is why even the first covenant was inaugurated with blood.