A key is symbolic of power, authority, influence, position, etc. that only the kingdom can give. The key to the kingdom is being born again. When you get born again, that is not the end of the road. You should acquire revelation so as to have the keys of the kingdom. There are various keys of the kingdom but the key to the kingdom is salvation.
Until you receive the keys of the kingdom you are not qualified to represent the kingdom on the earth. Actually there is no way we will be able to live like a child of God without having the keys of the kingdom. God is looking for representatives on the earth but you must have the keys.
One of the keys of the kingdom is binding and loosing, verse 19. As you represent God on the earth ,you will have the keys of the kingdom and whatever you bind shall be bound and whatever you loose shall be loosed. You have to bind (which also means to banishly stop) the things that the devil is releasing and doing. And loose what God is doing that the devil is opposing. To do these you must have the keys of the kingdom. Take note that binding and losing should not be your goal but the keys of the kingdom because binding and loosing came out of receiving the keys of the kingdom which comes by the revelation of Christ as the son of the living God.
You must ask yourself, ‘What are those keys of the kingdom and do I have them?” You must also find out how to receive them. There is no way to effectively represent God on the earth without having these keys.