The Pope was the successor of St. Peter, and the centre of unity in the Roman Catholic Church. Therefore he had an authority beyond that of all other ministers. Men have only so much authority as other men will allow; and the question of the extent of this spiritual authority, or its limitations, was a delicate discussion carried on by the Latin tongue in Spanish and French and German and Italian lecture-rooms. But everyone agreed that this was the vicar of Christ, and that his authority extended, or could in certain circumstances extend, as far as the authority of the whole Catholic Church.
So much was received by many Catholics before the Reformation. The events of Reformation and Counter-Reformation strengthened this pillar of the constitution. Radicals who denied the Pope's spiritual authority no longer claimed to be within the Roman Catholic Church and therefore need no longer be considered. The defence of Catholicism against Protestants had something of the same effect as, two or three centuries before, the defence of Christendom from Arab or Turk. It made the centre of Catholicism more supreme as the centre. It identified Catholicism more manifestly with Rome; so that when a Protestant used the word Catholic, he might henceforth be presumed to mean Roman Catholic.
This authority was defined to rest upon Bible and Church. In fact it rested upon the profession of Catholic faith by most ordinary men and women in the Catholic states. The Spanish confessed that the Pope was the head of their Church. Through their long struggle against Muslim invasion they identified their Church with their nationality, so that a Spaniard not a Catholic was no longer a Spaniard. Therefore the Pope had real power inside Spain, not just theoretical power or spiritual power derived from a theological principle or the explanation of a text of the Bible about the keys of St. Peter. In certain matters the Spanish government could hardly act without first making sure that the authorities of the Church agreed with its action. And so, though less obviously, in Portugal, France, Italy, Austria, and the south-German states.