Matthew 16:19

τὰς κλεῖδας τῆς βασιλείας τῶν οὐρανῶν. This expression was not altogether new. To a Jew it would convey a definite meaning. A key was given to a Scribe when admitted to his office as a symbol of his authority to open the treasury of the divine oracles (ch. Matthew 13:52). Peter was to be a Scribe in the kingdom of heaven. He has received authority to teach the truths of the kingdom. Again the key was symbolic of office and authority generally; cp. Isaiah 22:22 : ‘The key of the house of David will I lay upon his shoulder, &c.’—words which are transferred to Christ Himself Revelation 3:7. These words of his Lord would afterwards gain a fresh force for Peter, when he found that through him God had opened ‘the door of faith to the Gentiles.’ Acts 14:27.

ὃ ἐὰν δήσῃς κ.τ.λ. ‘To bind’ (cp. ch. Matthew 23:4) is to impose an obligation as binding; ‘to loose’ is to declare a precept not binding. Such expressions as this were common: ‘The school of Shammai binds it, the school of Hillel looses it.’ The power is over things, not persons. The decisions of Peter, as an authorized Scribe of the Kingdom of God will be ratified in heaven. Such decisions of the Scribes of the Kingdom of Heaven were the sentence pronounced by James, Acts 15:19, and the judgments of Paul in the Corinthian Church.

Compare with this passage John 20:23, λάβετε πνεῦμα ἄγιον, ἄν τινων�· ἄν τινων κρατῆτε κεκράτηνται, where the reference is to the judicial authority of the apostles; here a legislative power is conferred. Observe carefully the force of the perfect ἀφέωνται and κεκράτηνται, ‘whosesoever sins ye shall remit, they have been remitted.’ Your spiritual σύνεσις will enable you to recognise and ratify the divine judgment on offending persons. So here note the future perfect ἔσται δεδεμένον. your decision will have been anticipated in heaven.