The investiture conflict that emerged in the Medieval Europe, including England, marked the consistent shift in the view on the royal power and church in the society. In this regard, Henry IV denounced the Pope as a “false monk” because he stood on the ground that he, Henry IV, was the monarch, whose was granted to him by God directly, whereas Pope Gregory stood on the traditional ground that the church and he, as the head of the Roman Catholic Church, was the mediator between God and believers. From this angle, Henry IV was just a believer, whose power was limited by the civil law, whereas the divine law was the prerogative of the Roman Catholic Church and the Pope. Henry IV denied this view on his power and eliminated the Pope as a mediator between him and his power and God denouncing the Pose as “false monk”.
In fact, the conflict between Pope Gregory and King Henry IV revealed the full extent to which views of the Pope and the King on the political power varied. Henry IV denied any possibility of interference of the Pope in his politics, whereas Pope IV believed that monarchs, including Henry IV, should coordinate their policies with the Roman Catholic Church and him in person because religion still played an important part in the life of people and the Pope was responsible for believers, which were also subordinated to the King, but the Pope stood on the ground that he was a mediator, who maintained the communication between God and believers, among which the King was just one of believers.
Blumenthal, Uta-Renate. The Investiture Controversy: Church and Monarchy from the Ninth to the Twelfth Century. University of Pennsylvania Press, 1988.
Cowdrey, H.E.J. Pope Gregory VII, 1073–1085. Oxford University Press, 1998.