In order to bring some semblance of order out of heedless mob action it was of first importance to determine the exact beliefs and practices of the major dissident sects – the Cathars and the Waldensians – and the supporting reasons why they so believed. These doctrines were then compared with the teachings of the Roman Church, for both groups claimed that they were the true Christians trying to recapture the original, the pristine faith of the church, the faith of the Apostles. To the extent that their creeds were found to differ from the Catholic Church, the new movements were terms heretical. The purpose of the investigation, the ‘inquisitio’, was to point out to the dissenters wherein their teachings strayed from that of the Roman Church and hopefully, to win them back to their former allegiance. If a wayward son or daughter acknowledged his/her error and was received back into full communion with the Church, success was achieved. A salutary penance was given to the penitent – as is done today in the Sacrament of Penance. On the other hand, if the person knowingly and adamantly persisted in his/her heterodox beliefs, the Church then sorrowfully acknowledged defeat, solemnly declared the person a heretic, removed him/her from the communion of the faithful, and handed him/her over to the Secular Power to answer for the crime of disloyalty committed against political society.
In this way the faithful were protected from the contagion of evil doctrine, and the State preserved the integrity of the political and social order. For in the thirteenth century, and long before, Church and State worked closely together to protect and maintain the religious, social, and political stability that all believed necessary for the commonweal. In principle the separation of Church and State was insisted upon, even though the close interdependence of one on the other brought them into continuous association. The Church became heavily entangled in the feudal system, so much so that its ministers, even bishops, were chosen by the State and its property handled at times as a private possession by lay expropriators. It was only a mighty effort by the Gregorian Reform that reversed this stranglehold. The State in its turn had depended enormously on the Church for its legitimacy, for its higher trained officials and for the only education and culture that existed. Therefore, the unity of Christendom was sundered not only by the anti-ecclesiastical attitude of these new heretical sects, but by their anti-social nature as well (marriage was evil, all oaths upon which feudalism depended were prohibited, the coercive power of political authorities was denied – all of which undermined the very existence of organized society). In the twentieth century this kind of correlation and consensus simply does not exist.
Albert Shannon, The Medieval Inquisition (1991)