An instrument used to lock or unlock doors and gates. “Key” is used both literally and figuratively in the Bible.

The key of Biblical times was often a flat piece of wood having pins that corresponded to holes in a bolt that was inside the door of a home. Such a key served to push the bar or bolt inside the door, instead of being turned in the lock as is the modern key. The key was often carried in the girdle or was fastened to some other object and carried over the shoulder.​—Isa 22:22.

Egyptian keys of bronze or iron have been found, consisting of a straight shank approximately 13 cm (5 in.) long, with three or more projecting teeth at the end. The Romans also used metal keys, including some of the type made to turn in locks. Keys of bronze have been discovered in Palestine.

Moabite King Eglon used a lock and key for the door of his roof chamber. (Jg 3:15-17, 20-25) Certain postexilic Levites were entrusted with temple guard service, being placed “in charge of the key, even to open up from morning to morning.”​—1Ch 9:26, 27.

Figurative Use. In the figurative vein the Bible uses the term “key” to symbolize authority, government, and power. Eliakim, elevated to a position of trust and honor, had “the key of the house of David” put upon his shoulder. (Isa 22:20-22) In the Middle East, in more recent times, a large key upon a man’s shoulder identified him as a person of consequence or importance. Anciently, a king’s adviser, entrusted with the power of the keys, might have general supervision of the royal chambers and might also decide on any candidates for the king’s service. In the angelic message to the congregation in Philadelphia the exalted Jesus Christ is said to have “the key of David,” and he is the one “who opens so that no one will shut, and shuts so that no one opens.” (Re 3:7, 8) As the Heir of the covenant made with David for the Kingdom, Jesus Christ has committed to him the government of the household of faith and the headship of spiritual Israel. (Lu 1:32, 33) By his authority, symbolized by “the key of David,” he can open or shut figurative doors, or opportunities and privileges.​—Compare 1Co 16:9; 2Co 2:12, 13.

How did Peter use “the keys of the kingdom” that were entrusted to him?

Jesus said to Peter: “I will give you the keys of the kingdom of the heavens, and whatever you may bind on earth will be the thing bound in the heavens, and whatever you may loose on earth will be the thing loosed in the heavens.” (Mt 16:19) The identification of these keys logically must be based on other Scriptural information. Jesus made another reference to the subject of keys when he said to the religious leaders, versed in the Law, “You took away the key of knowledge; you yourselves did not go in, and those going in you hindered!” (Lu 11:52) A comparison of this text with Matthew 23:13 indicates that the ‘going in’ referred to is with regard to entrance into “the kingdom of the heavens.” Thus, the use of the word “key” in Jesus’ statement to Peter indicated that Peter would have the privilege of initiating a program of instruction that would open up special opportunities with respect to the Kingdom of the heavens.

Different from the hypocritical religious leaders of that time, Peter clearly did use divinely provided knowledge to help persons to ‘enter into the kingdom,’ notably on three occasions. One was on the day of Pentecost 33 C.E., when Peter, under inspiration, revealed to a gathered multitude that Jehovah God had resurrected Jesus and exalted him to His own right hand in the heavens and that Jesus, in that royal position, had poured out holy spirit on his assembled disciples. As a result of this knowledge and acting upon Peter’s exhortation, “Repent, and let each one of you be baptized in the name of Jesus Christ for forgiveness of your sins, and you will receive the free gift of the holy spirit,” about 3,000 Jews (and Jewish converts) took the step that led to their becoming prospective members of “the kingdom of the heavens.” Other Jews subsequently followed their example.​—Ac 2:1-41.

On another occasion Peter and John were sent to the Samaritans, who had not received the holy spirit even though they had been baptized. However, the two apostles “prayed for them” and “went laying their hands upon them,” and they received holy spirit.​—Ac 8:14-17.

The third occasion of Peter’s being used in a special way to introduce persons into privileges as Kingdom heirs was when he was sent to the home of the Gentile Cornelius, an Italian centurion. By divine revelation Peter recognized and declared God’s impartiality as regards Jews and Gentiles and that people of the nations, if God fearing and doers of righteousness, were now as acceptable to God as their Jewish counterparts. While Peter was presenting this knowledge to his Gentile hearers, the heavenly gift of the holy spirit came upon them and they miraculously spoke in tongues. They were subsequently baptized and became  the first prospective members of “the kingdom of the heavens” from among the Gentiles. The unlocked door of opportunity for Gentile believers to become members of the Christian congregation thereafter remained open.​—Ac 10:1-48; 15:7-9.

Matthew 16:19 may be rendered with grammatical correctness: “Whatever you may bind on earth will be the thing bound [or, the thing already bound] in the heavens, and whatever you may loose on earth will be the thing loosed [or, the thing already loosed] in the heavens.” The translation by Charles B. Williams here reads: “Whatever you forbid on earth must be what is already forbidden in heaven, and whatever you permit on earth must be what is already permitted in heaven.” Greek scholar Robert Young’s literal translation reads: “Whatever thou mayest bind upon the earth shall be having been bound in the heavens, and whatever thou mayest loose upon the earth shall be having been loosed in the heavens.” Since other texts make clear that the resurrected Jesus remained the one true Head over the Christian congregation, it is obvious that his promise to Peter did not mean Peter’s dictating to heaven what should or should not be loosed but, rather, Peter’s being used as heaven’s instrument in the unlocking, or loosing, of certain determined things.​—1Co 11:3; Eph 4:15, 16; 5:23; Col 2:8-10.

“Key of the abyss.” At Revelation 9:1-11 the vision is presented of “a star” out of heaven to whom “the key of the pit of the abyss” is given and who opens that pit and releases a swarm of locusts, their king being “the angel of the abyss.” Since the abyss, as shown at Romans 10:6, 7, evidently includes Hades (though it is not limited to Hades), it appears that “the key of the pit of the abyss” includes “the keys of death and of Hades” possessed by the resurrected Jesus Christ, as stated at Revelation 1:18. These “keys” are undoubtedly symbolic of Jesus’ authority to free persons from a restraint that is beyond the power of anyone but God or his authorized representative. The “keys” therefore include authority to resurrect persons literally, freeing them from the confines of the grave, as well as to release persons from a figurative death state. (Joh 5:24-29; compare Re 11:3-12; see DEATH [Change in spiritual state or condition].) The last-recorded use of “the key of the abyss” is at Revelation 20:1-7, where the vision describes an angel with that key casting Satan into the abyss, shutting and sealing it over him for a thousand years. At the close of that period Satan is released from his “prison,” evidently by the use of the “key” of authority.​—See ABYSS.