Do you know where the Western idea that kings/governments do not have unlimited power comes from? The idea that kings and governors are LIMITED in their authority is a Biblical, theonomic idea. The idea being that even the king is a SUBJECT of the Word of God, that government is limited by the Word of God.
Now, suppose we reject a theonomic and Biblical worldview. What then will limit government? Constitutions? Constitutions are written by men, interpreted by men, amended by men, re-written by men, abolished by men... In other words, without a Divine Standard, ultimately anything goes. If men are to be responsible for coming up for the boundaries of their powers, then there will in the end be no limit to their power. They will legislate on whatever suits their fancy, in whatever way they think they can get away with.
It is in fact preposterous to think that men can be trusted to set the boundaries of their own powers. Men are evil, wicked sinners. They therefore cannot be trusted to legislate out of their own hearts. They must therefore be limited to enforcing God's Law, for He is the Lawgiver, not men.
"Kings then have not an absolute power, to do in their government what pleases them, but their power is limited by God's word; so that if they strike where God has not commanded, they are but murderers; and if they spare where God has commanded to strike, they and their throne are criminal and guilty of the wickedness which abounds upon the face of the earth, for lack of punishment." - John Knox, a Sermon on
Isaiah 26 -
http://biblehub.com/library/knox/the...saiah_xxvi.htm