The Church is defined as "a divinely-instituted community of men, united by the orthodox faith, the law of God, the hierarchy and the sacraments."
Medieval speculation took the Church and the Empire for granted, as divinely appointed institutions, under which the nations of the earth must flourish for the space of man's probation on this planet.
The bishop of Rome, who had from the first probably enjoyed a leading position in the Church as " the successor of the two most glorious of the apostles," elaborated his claims to be the divinely appointed head of the ecclesiastical organization.
Gregory's position was almost inexpugnable at a time when it was conceded by practically all that spiritual concerns were incalculably more momentous than secular, that the Church was rightly one and indivisible, with one divinely revealed faith and a system of sacraments absolutely essential to salvation.
Thomas Aquinas was the first theologian to describe the Church as a divinely organized absolute monarchy, whose head concentrated in his person the entire authority of the Church, and was the source of all the ecclesiastical law (conditor juris), issuing the decrees of general councils in his own name, and claiming the right to revoke or modify the decrees of former councils - indeed, to make exceptions or to set aside altogether anything which did not rest upon the dictates of divine or natural law.