Remembering that sin brought death on all of humanity through Adam, why then were animals sacrificed. After all, they did nothing wrong. In fact, animals can't sin because they aren't moral beings like us. Only humans know better and yet we disobey God.
The heavenly Father often uses imagery to graphically teach us truths. One of those is the sinfulness of sin. The sacrifice of animals can't pay the penalty for our rebellion against god but they were a sort of spiritual IOU. The entire eleventh chapter of Hebrews describes how those Old Testament saints looked forward to the coming messiah who would save humanity. Animal sacrifices indicated to the Old Testament believers that an innocent person, namely Jesus, would take our punishment.
We also see in the Bible that the first animal to be killed for humanity provided covering for Adam and Eve's shame. Genesis 3:21 (KJV) says, "Unto Adam also and to his wife did the LORD God make coats of skins, and clothed them."
Furthermore, the requirements of perfect sacrificial animals was a picture of how the Lord wants his church to be. Hebrews 9:14 (KJV) states, "How much more shall the blood of Christ, who through the eternal Spirit offered himself without spot to God, purge your conscience from dead works to serve the living God?"
So the offering of animals wasn't some sort of cruel rule imposed upon the Israelites by a mean deity but the Father's graphic warning of sin's dire consequences. Christ became the spiritual perfect lamb of God and died in the place of whoever surrendered themselves to his rulership. What an awesome gift salvation is.
I'm currently writing a book called You Think You're Going to Heaven? It warns people to be absolutely sure of their hope in heaven. Watch this space for updates as well as posts on the topic of heaven.