Why Does God Require Sacrifice after Sin?

Questions about why God requires sacrifice after sin, why God had to adhere to sin’s death penalty such that he had to devise a plan of substitutionary atonement, and how we’re able to grieve the Holy Spirit with our sin if God doesn’t see our sin.

• Why does God require sacrifice after sin, and is Genesis 3:21 an example of this?
• Why does sin have the power of death, and why did God have to adhere to sin’s death penalty such that he had to devise a plan of substitutionary atonement?
• If God doesn’t see our sin because of the blood of Jesus, how are we still able to grieve the Holy Spirit when we sin?