'Key' in the Bible

“And to the angel (divine messenger) of the church in Philadelphia write:“These are the words of the Holy One, the True One, He who has the key [to the house] of David, He who opens and no one will [be able to] shut, and He who shuts and no one opens:

Then the fifth angel sounded [his trumpet], and I saw a star (angelic being) that had fallen from heaven to the earth; and the key of the bottomless pit (abyss) was given to him (the star-angel).

And then I saw an angel descending from heaven, holding the key of the abyss (the bottomless pit) and a great chain was in his hand.