I have this from Mark Bonocore but haven’t verified his quotations:
(
snipped)
St. John Cassian (c. 362-435), who writes:
“O Peter, Prince of Apostles, it is just that you should teach us, since you were yourself taught by the Lord; and also that you should open to us the gate of which you have received
the Key (singular).
Keep out all those who are undermining the heavenly House; turn away those who are trying to enter through false caverns and unlawful gates since it is certain that no one can enter in at the gate of the Kingdom except the one unto whom
the Key (singular), placed by you in the churches, shall open it.” (John Cassian, Book III, Chap 12, Against the Nestorians on the Incarnation)
Compare this to Isaiah 22, which reads:
“On that day I shall summon my servant Eliakim, son of Hilkiah. …I will place
the Key of the House of David on his shoulder; when he opens, no one shall shut, and when he shuts, no one shall open.”
Cassian is clearly drawing from Isaiah 22, and applying it to Matt 16.
I believe the reason we don’t see Isaiah 22 used more extensively is that it’s rooted in a sense of Jewish national identity. And, since most of the fathers were Gentiles, it’s not surprising that they see the Keys of Matt 16 referring to authority in a more generic sense (which is equally valid). However, we do see the Kingly, Davidic aspect of the Keys alluded to more often in the Semetic-speaking branches of the Church. For example, Aphraates the Sage (c. 330 A.D.), one of the oldest fathers of the Syrian Church, says:
“
David handed over the Kingdom to Solomon and was gathered to his people; and Jesus handed over the Keys to Simon and ascended and returned to Him Who sent Him.” (Aphraates, xxi, 13).
Also, St. Ephraem the Syrian (c. 350) writes:
“
Then Peter deservedly received the Vicariate of Christ over His people.” (Ephraem, Sermon de Martyrio. SS. App. Petri et Pauli).
From
Answer to James White on the Early Papacy