The Kingdom is the rule of God, rule according to His will. The Law of God is the expression of that will. God rules according to law, law that it not arbitrary but the transcript of His own divine character.
Law thus lies at the heart of the Kingdom.
Obedience to that law is the claim put upon all creatures, because they are subjects of the King who created them. His rational creatures are expected to obey Him out of their own free will. As they have a choice in the matter, they have the potential for being more than blindly obedient, but to be willingly obedient. Obedience from the heart is the essence of life in the Kingdom. The institutional church is the body of citizens who share public authority, who in gathering together in their official capacity participate in the rule of the King.