The skin covering is help that god supplies after the fall. Adam and Eve tried to cover their sin, but god showed forgiveness in the shedding of blood (not just any blood, but the blood of Christ His son).Many things in Gods word can be taken literal, but yet also has Spiritual implications. Example: God made skins to cover Adam, (literal), but yet it can be that of the Spiritual notation of God covering us in His righteousness (grace) that covers our shame (sin) as we are once again made righteous before Him.
Kidneys show removal of toxins / waste from body activity. Jesus received stripes that pierced his kidneys like arrows (by his stripes we were healed
I Peter 2:24 ).
The hidden man of the heart is symbolized by the natural pacemaker ( the natural nerve network pacemaker looks like a crucified cartoon man with all his bones out of joint). I sure agree the natural facts of creation point to spiritual knowledge Romans 1:19-20 .
Natural things point to reality. Adam naked, fig leafed, and covered with God's covering points to the future righteousness Jesus will provide. It also,IMHO, points out that Adam does not put on original Eden glory, but puts on a future glory yet to be revealed (revealed, at a point in time, through Jesus).
Again, Adam appears not to have the final great glory, but awaits that glory accomplished by Jesus. Corruption will put on in-couuuption, at the last trump.
eddif