Long before Adam and Eve were created, God provided a remedy for sin that would not fail if seriously applied.
- Before their sin Adam and Eve were covered in innocence "with glory".
- In their sin they were covered with "aprons of fig leaves" -- man's own failing efforts to cover himself.
- After their sin they were covered with "coats of skins" -- God covering through the shedding of blood.
Romans 5:12,17 Wherefore as by one man sin entered the world, and death by sin; and so death passed upon all men, for that all have sinned.
For if by one man's offence death reigned by one; much more they which receive abundance of grace and of the gift of righteousness shall reign in life by one, Jesus Christ.
An innocent animal had to be slain to cover the nakedness of Adam and Eve. The innocent gave up his life for the guilty. It is a picture -- a symbol -- of the cross.