The answer is:
Kings on earth rule with the authority of God, because:
Bishops have always been important since the feudal era, they have had power and respect over people. The people thought that he was the person sent by God to lead his church.
The bishops had as much power as the feudal lords and their word was important at that time, sometimes they justified the king with his people so that the kings would be sent by God.
I hope it help you