In Old Testament kingdoms one man stood next to the king in authority. He was known as master of the palace, head of the household or keeper of the keys (to the palace). For some references to these officials, see 1 Kings 4:6; 16:9; 18:3; 2 Kings 15:5. Much farther back in history, Joseph was master of the palace of Pharaoh (see Gn 41:39-44). Isaiah 22:15-23 is especially informative in this regard. Appointing a new master of the palace for the kingdom of Judah, God said, “He shall be a father to the inhabitants of Jerusalem, and to the house of Judah. I will place the key of the House of David on his shoulder; what he opens, no one will shut, what he shuts, no one will open” (vv. 21-22).
Look again at Matthew 16. Jesus conferred an institutional authority. Now look at Matthew 18:18. Jesus conferred on all the apostles a pastoral authority. Two totally different realities. Notice the metaphors. One doesn’t “bind and loose” with keys, nor does one “open and shut” with pastoral authority.
John 21:15-17 is important, too. Three times Jesus gave a command to Peter. The first and third times Jesus commanded Peter, “Feed my sheep.” The verb is boske, which means “to feed.” In the second command Jesus said, “Tend my sheep.” The verb is poimaine, which means “to tend,” “to superintend,” “to direct.”
Again, just before His passion Jesus called on Peter to exercise his authority. He warned Peter against Satan’s onslaughts, and assured him, “But I have prayed that your own faith may not fail; and once you have turned back, you must strengthen the brothers [that is, the Christian community]” (Lk 22:31-32).