"I will give you the keys to the kingdom of heaven"
The Lord recognised in Peter a faithful steward to whom he entrusted the key of the Kingdom and, in Paul, a skilled master to whom he gave responsibility for teaching in the Church. So that those whom Paul has formed might find salvation, Peter must receive them into their rest. When Paul has opened hearts by his preaching, Peter will open the Kingdom of heaven to souls. So it is a kind of key that Paul, too, has received from Christ: the key of knowledge, enabling him to open up to their very depths hearts hardened towards the faith. Then, in spiritual unveiling, it causes what was hidden within to appear in the light of day. This is a key that allows the confession of sin to escape from consciences and locks within them for ever the grace of the Savior's mystery.
So both have received keys from the Lord's hands: the key of knowledge for the one and the key of authority for the other; the former metes out the riches of immortality, the latter dispenses treasures of wisdom. For there are treasures of knowledge, as it is written: this mystery is Christ “in whom are hidden all the treasures of wisdom and knowledge,” (Col 2:3).
St. Maximos the Confessor