Explica así porqué son importantes las herejías para entender la historia europea:
We must note that whether the complete scheme thus attacked be true or false is indifferent to the value of heresy as a department of historical study. What we are concerned with is the highly interesting truth that heresy originates a new life of its own and vitally affects the society it attacks. The reason that men combat heresy is not only, or principally, conservatism_a devotion to routine, a dislike of disturbance in their habits of thought_it is much more a perception that the heresy, in so far as it gains ground, will produce a way of living and a social character at issue with, irritating, and perhaps mortal to, the way of living and the social character produced by the old orthodox scheme.
The whole story of Europe, her various realms and states and general bodies during the last sixteen centuries has mainly turned upon the successive heresies arising in the Christian world.
We are what we are today mainly because no one of those heresies finally overset our ancestral religion, but we are also what we are because each of them profoundly affected our fathers for generations, each heresy left behind its traces, and one of them, the great Mohammedan movement, remains to this day in dogmatic force and preponderant over a great fraction of territory which was once wholly ours.
El segundo capítulo (Scheme of This Book) anuncia cuáles han sido las principales herejías:
The Arian heresy (filling the fourth, and active throughout the fifth, century), proposed to go to the very root of the Church’s authority by attacking the full Divinity of her Founder. But it did much more, because its underlying motive was a rationalizing of the mystery upon which the church bases herself: the Mystery of the Incarnation. Arianism was essentially a revolt against the difficulties attaching to mysteries as a whole though expressing itself as an attack on the chief mystery only. Arianism was a typical example on the largest scale of that reaction against the supernatural which, when it is fully developed, withdraws from religion all that by which religion lives.
The Mohammedan attack was of a different kind. It came geographically from just outside the area of Christendom; it appeared, almost from the outset, as a foreign enemy; yet it was not, strictly speaking, a new religion attacking the old, it was essentially a heresy; but from the circumstances of its birth it was a heresy alien rather than intimate. It threatened to kill the Christian Church by invasion rather than to undermine it from within.
The Albigensian attack was but the chief of a great number, all of which drew their source from the Manichean conception of a duality in the Universe; the conception that that good and evil are ever struggling as equals, and that Omnipotent Power is neither single nor beneficient. Closely intertwined with this idea and inseparable from it was the conception that matter is evil and that all pleasure, especially of the body, is evil. This form of attack, of which I say the Albigensian was the most notorious and came nearest to success, was rather an attack upon morals than upon doctrine; it had the character of a cancer fastening upon the body of the Church from within, producing a new life of its own, antagonistic to the life of the Church and destructive of it_just as a malignant growth in the human body lives a life of its own, other than, and destructive of, the organism in which it has parasitically arisen.
The Protestant attack differed from the rest especially in this characteristic, that its attack did not consist in the promulgation of a new doctrine or of a new authority, that it made no concerted attempt at creating a counter-Church, but had for its principle the denial of unity. it was an effort to promote that state of mind in which a <Church> in the old sense of the word_that is, an infallible, united, teaching body, a Person speaking with Divine authority_should be denied; not the doctrines it might happen to advance, but its very claim to advance them with unique authority. Thus, one Protestant may affirm, as do the English Puseyites, the truth of all the doctrines underlying the Mass_the Real Presence, the Sacrifice, the sacerdotal power of consecration, etc._another Protestant may affirm that all such conceptions are false, yet both these Protestants are Protestant because they communicate in the fundamental conception that the Church is not a visible, definable and united personality, that there is no central infallible authority, and that therefore each is free to choose his own set of doctrines.
Such affirmations of disunion, such denial of the claim to unity as being part of the Divine order, produced indeed a common Protestant temperament through certain historical associations; but there is no one doctrine nor set of doctrines which can be affirmed as being the kernel of Protestantism. Its essential remains the rejection of unity through authority.
Lastly there is that contemporary attack on the Catholic Church which is still in progress and to which no name has been finally attached, save the vague term «modern.» I should have preferred, perhaps, the old Greek word «alogos»; but that would have seemed pedantic. And yet it is a pity to have to reject it, for it admirably describes by implication the quarrel between the present attackers of Catholic authority and doctrine, and the tone of mind of a believer. Antiquity began by giving the name «alogos» to those who belittled or denied, though calling themselves Christians, the Divinity of Christ. They were said to do so from lack of «wit,» in the sense of «fullness of comprehension,» «largeness of apprehension.» Men felt about this kind of rationalism as normal people feel about a colour-blind man.
Trataremos de cada una de ellas en mas detalle.