What happens when a ruler wants to take over the Church? Our saint today had that problem back in the eleventh century. Pope St. Gregory VII was pope at a time when the emperor was trying to control the Church through his investing of authority to bishops. If Emperor Henry IV could "hire" the bishops, then he could control them and rule them, and the Church, the way he ruled the empire. This corrupt use of power was called lay investiture, giving authority to leaders of the Church by lay rulers.
Pope St. Gregory VII was a reforming pope. Before he became pope he was an advisor to popes in their efforts to help the Church retain their religious rights and liberties against local rulers who wanted to make those bishops and abbots another part of the government. Gregory excommunicated Henry at one point, but Henry repented and Gregory lifted the excommunication. Whereupon, Henry consolidated his power, gathered his forces, arrested Gregory, and exiled him, where Gregory died.
The Church as the right to minister as she sees fit without restriction by the government. She has the right to teach the faith. She has the right to choose who may teach the faith and the right to require those teachers to be faithful to her teachings. She as the right to serve the poor without being required to follow the latest government dogmas on a new and unjust standard of equality. She has the right to speak out against injustices perpetrated by the government. Pope St. Gregory VII would recognize ours as a time of struggle between Church and State. Pope St. Gregory VII, pray for us.