Matthew 16:19 (KJV)
And I will give unto thee the keys of the kingdom of heaven: and whatsoever thou shalt bind on earth shall be bound in heaven: and whatsoever thou shalt loose on earth shall be loosed in heaven.
Having the key(s) to anything infers being locked out of something or some place to begin with. And that the key(s) are the initial opening / unlocking. The lock between heaven and hell is the Lord
Jesus:
John 3:16–18 (KJV)
16 For God so loved the world, that he ga