Several sections deal with the Keys of the Kingdom and binding and loosing.
Around the section dedicated to the creed on “Forgiveness of Sins,” it talks about the “power of the keys,” which has historically been associated with the Church’s authority to forgive sins. This is an ancient teaching. As far back as Tertullian do we see theologians associate the Keys with absolution of sins.
But more generally, the power of the Keys of the Kingdom is the ability of Christ’s stewards, particularly the chief steward — the Pope — to act and rule on his behalf. The quote from Jesus is a reference to Isaiah 22:22 (I think that is the correct verse, I may be wrong – it’s in Isaiah), which talks about the chief steward or prime minister who rules with the “key” under the authority of the Davidic king.