The keys of the kingdom represents the power Christ has given to the legitimate leaders of His Church to discipline (binding) and disciple (loosing), all according to the Word of God.
When a person comes into the congregation with a strange teaching that contradicts the Bible, they are not to be tolerated. Conversely, the leaders have the responsibility to faithfully teach all and only what is found in the Word of God. That is their divine authority.
This is why it is important to have a plurality of leaders (elders) in the Church. The decision is never left to any one man. There is wisdom in numbers (Proverbs 11:14; 15:22; 24:6).
So why is the term kingdom used?
Is the church the kingdom? Does the church determine who gets to the kingdom.