Key

Holding a key means holding authority. In Isaiah 22, “he shall open, and none shall shut.” Revelation 3 uses almost the same words for Jesus, who has “the key of David.” In Matthew 16, he promises Peter “the keys of the kingdom of heaven,” and in Revelation 1 he says he holds “the keys of hell and of death.” Luke 11 gives a sharper turn, when Jesus warns teachers who “have taken away the key of knowledge.” Christians read these passages in different ways, especially the one about Peter.

6 verses

Isaiah

Isaiah 22:22

And the key of the house of David will I lay upon his shoulder; so he shall open, and none shall shut; and he shall shut, and none shall open.

Matthew

Matthew 16:19

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.

Luke

Luke 11:52

Woe unto you, lawyers! for ye have taken away the key of knowledge: ye entered not in yourselves, and them that were entering in ye hindered.

Revelation

Revelation 1:18

I am he that liveth, and was dead; and, behold, I am alive for evermore, Amen; and have the keys of hell and of death.

Revelation 3:7

And to the angel of the church in Philadelphia write; These things saith he that is holy, he that is true, he that hath the key of David, he that openeth, and no man shutteth; and shutteth, and no man openeth;

Revelation 9:1

And the fifth angel sounded, and I saw a star fall from heaven unto the earth: and to him was given the key of the bottomless pit.

From Easton's Bible Dictionary

Matthew George Easton, 1897

Frequently mentioned in Scripture. It is called in Hebrew maphteah, i.e., the opener (Judg. 3:25); and in the Greek New Testament kleis, from its use in shutting (Matt. 16:19; Luke 11:52; Rev. 1:18, etc.). Figures of ancient Egyptian keys are frequently found on the monuments, also of Assyrian locks and keys of wood, and of a large size (comp. Isa. 22:22).

The word is used figuratively of power or authority or office (Isa. 22:22; Rev. 3:7; Rev. 1:8; comp. 9:1; 20:1; comp. also Matt. 16:19; 18:18). The “key of knowledge” (Luke 11:52; comp. Matt. 23:13) is the means of attaining the knowledge regarding the kingdom of God. The “power of the keys” is a phrase in general use to denote the extent of ecclesiastical authority.

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From Smith's Bible Dictionary

William Smith, 1884

The key of a native Oriental lock is a piece of wood, from seven inches to two feet in length, fitted with the wires or short nails, which, being inserted laterally into the hollow bolt which serves as a lock, raises other pins within the staple so as to allow the bolt to be drawn back. (Keys were sometimes of bronze or iron, and so large that one was as much as a man could carry. They are used in Scripture as a symbol of authority and power. Giving keys to a person signifies the intrusting of him with an important charge. (Matthew 16:19) In England in modern times certain officers of the government receive, at their induction into office, a golden key. --ED.)