Keys.  Fascinating in their simplicity, mystifying in their cut.  Of all keys, the Master Key is most desirable.  If the Great Keymaker were to bestow Master Key status on One Human Being, what would that person do with the power to open the innermost parts of his fellow beings?  How would he use that power?  For opening is only that, while entering presents many more questions.  Will he scorn, honor, deride, embrace, or perhaps worst, ignore what he would find inside? 
Mythology or folklore communicates, I suspect, the wisdom that only the “worthy one” acquires the Master Key.  Only the “pure of heart” would be entrusted with so much responsibility.  For opening is only the first step on a journey of loving whatever is found within, and what is found within is horrifying and corrupt many times. 
Christianity is the story of the Great Keymaker bestowing the Key to the God-Man Jesus, who could be entrusted to enter into the human soul, see there the disease and disorientation, and embrace it, heal it, restore it to health and eternal life.  So he said to his disciples, having loved them, even as He was loved, “I will give you the keys to the Kingdom of Heaven.”  Matt. 16:19.