““Elsewhere in Scripture we learn that without the shedding of blood there is no remission of sins (Hebrews 9:2222), and the life of the flesh is in the blood (Leviticus 17:1123). Because Adam sinned, a payment for sin was needed. Because sin’s penalty was death, then death and bloodshed were needed to atone for sin. So Genesis 3:21 would describe the first blood sacrifice as a penalty for sin — looking forward to the One who would die “once for all” (Hebrews 10:10–1424).””
