Why was the blood shed from sacrificial animals in Genesis?
After Adam believed what God said, the blood was shed from sacrificial animals to provide a covering. It covered their physical bodies and also clothed them with a spiritual garment that hid old Adam, signifying the imputed righteousness of God.
Les explains that because Adam had the ability to believe what God said, the blood has now been shed from the sacrificial animals. He not only covers their physical body, but He clothes them with a spiritual garment that now hid old Adam, and he now has the imputed righteousness of the righteousness of God. Les connects this with Isaiah 61:10 and Romans 3, saying when He clothed Adam, when He clothed Isaiah, and when He clothes a believer in Romans 3, it is all the same thing: the imputed righteousness of God. Isaiah rejoices because God clothed him with the garments of salvation.