After Adam and Eve sinned,

“Then the eyes of both of them were opened, and they realized that they were naked. So, they sewed fig leaves together to make themselves loincloths.” Genesis 3:7. CJB

This type of cover was not going to last so, Elohim made for them:

“Adonai, Elohim, made garments of skin for Adam and his wife and clothed them.” Genesis 3:21. CJB

However, a covering of skin was also not going to last since Elohim instituted blood for life and purification. The altar of burnt offerings represented the blood sacrifice of an animal for cleansing of sins. 

Why animals?

Because; the Israelites had to know that something had to die for them to have life and be cleansed from impurity or sin.

The burnt offering was the foreshadowing of Yeshua being the ultimate blood sacrifice, which He did once and for all.

Through his Obedience and humbleness,

“…..he emptied himself, in that he took the form of a slave by becoming like human beings are. And when he appeared as a human being, 8 he humbled himself still more by becoming obedient even to death; death on a stake as a criminal!” Philippians 2:7-8. CBS.