The explanation is not difficult to find.  It is contained in a story of sin and shame.  I prefer, therefore, in the following paragraphs, to offer explanatory facts derived from Catholic authors, and, indeed, to present them as nearly as I can in the words of those writers.

The story I am about to relate is a narrative of the transformation of a confederacy into an absolute monarchy.

In the early times every church, without prejudice to its agreement with the Church universal in all essential points, managed its own affairs with perfect freedom and independence, maintaining its own traditional usages and discipline, all questions not concerning the whole Church, or of primary importance, being settled on the spot.

Until the beginning of the ninth century, there was no change in the constitution of the Roman Church.  But about 845 the Isidorian Decretals were fabricated in the west of Gaul—­a forgery containing about one hundred pretended decrees of the early popes, together with certain spurious writings of other church dignitaries and acts of synods.  This forgery produced an immense extension of the papal power, it displaced the old system of church government, divesting it of the republican attributes it had possessed, and transforming it into an absolute monarchy.  It brought the bishops into subjection to Rome, and made the pontiff the supreme judge of the clergy of the whole Christian world.  It prepared the way for the great attempt, subsequently made by Hildebrand, to convert the states of Europe into a theocratic priest-kingdom, with the pope at its head.

Gregory VII., the author of this great attempt, saw that his plans would be best carried out through the agency of synods.  He, therefore, restricted the right of holding them to the popes and their legates.  To aid in the matter, a new system of church law was devised by Anselm of Lucca, partly from the old Isidorian forgeries, and partly from new inventions.  To establish the supremacy of Rome, not only had a new civil and a new canon law to be produced, a new history had also to be invented.  This furnished needful instances of the deposition and excommunication of kings, and proved that they had always been subordinate to the popes.  The decretal letters of the popes were put on a par with Scripture.  At length it came to be received, throughout the West, that the popes had been, from the beginning of Christianity, legislators for the whole Church.  As absolute sovereigns in later times cannot endure representative assemblies, so the papacy, when it wished to become absolute, found that the synods of particular national churches must be put an end to, and those only under the immediate control of the pontiff permitted.  This, in itself, constituted a great revolution.