Genesis 3:21

Many have claimed that this passage is about God teaching that blood must be shed for a sacrifice and a covering for sin, as well as the need for a substitute. However, not a single Bible verse references this passage, nor is there anything special beyond God making these animal skins. The passage also says nothing about which animal the skins came from. They could have come from any animal with leathery skin—maybe the skins were from kangaroos or horses. Nothing is said about God using the occasion as a lesson about making sacrifices. It is more reasonable to imagine that God used this opportunity to show them that it is acceptable to kill an animal for our needs, and also how to cover themselves efficiently and effectively, but even this is not stated. We should not build theological systems on speculative ideas that are not in the text.