KEY
In the East (Judges 3:25) it was a piece of wood that was used to lift or move the bar that closed the door behind. The key wouldn’t turn.
It was worn on the waist or, sometimes, due to its large size, carried on the shoulder. They could measure from 15 to 60 cm. in length (cf. Is. 22:22).
Symbolically they use the authority of opening and closing. Eliakim, in the already cited passage of Is. 22:22, is a type of the Lord Jesus as he appears in Rev. 3:7, who has the keys of Hades and death (Rev. 1:18).
Peter was given the keys to the kingdom of heaven (Mt. 16:19). He fulfilled its function by opening it to the Jews (Acts 2) and the Gentiles (Acts 10). The Lord accused the doctors of the law of taking away the key of knowledge (Lk. 11:52).
They did this through their traditions and by making it difficult for those who would have wanted to enter into the blessings offered and achieved by Christ.