Genesis 8:20

An *altar was a pile of stones like a table. Noah made a fire on the *altar and he burned the animals. They were a gift to God. Many ancient people burned animals. They were *offerings to God.

The animals died as a sign that Christ would die on the cross. Nowadays, we put our trust in Christ, who saves us. God’s ancient people did not know about Christ. So God told them to kill animals as *offerings. Each animal that they killed was a sign of Christ.

For ‘clean’ see the comment on Genesis 7:2.