There's a song that I learned in church camp many years ago. The chorus goes "And they'll know we are Christians by our love, by our love. And they'll know we are Christians by our love".
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Church legislation on heresy
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This legislation remained in force and with even greater severity in the kingdom formed by the victorious barbarian invaders on the ruins of the Roman Empire in the West. The burning of heretics was first decreed in the eleventh century. The Synod of Verona (1184) imposed on bishops the duty to search out the heretics in their dioceses and to hand them over to the secular power. Other synods, and the Fourth Lateran Council (1215) under Pope Innocent III, repeated and enforced this decree, especially the Synod of Toulouse (1229), which established inquisitors in every parish (one priest and two laymen). Everyone was bound to denounce heretics, the names of the witnesses were kept secret; after 1243, when Innocent IV sanctioned the laws of Emperor Frederick II and of Louis IXagainst heretics, torture was applied in trials; the guilty persons were delivered up to the civil authorities and actually burnt at the stake. Paul III (1542) established, and Sixtus V organized, the Roman Congregation of the Inquisition, or Holy Office, a regular court of justice for dealing with heresy and heretics (seeROMAN CONGREGATIONS). The Congregation of the Index, instituted by St. Pius V, has for its province the care of faith and morals in literature; it proceeds against printed matter very much as the Holy Office proceeds against persons (see INDEX OF PROHIBITED BOOKS). The present pope [1909], Pius X, has decreed the establishment in every diocese of a board of censors and of a vigilance committee whose functions are to find out and report on writings and persons tainted with the heresy of Modernism (Encyclical "Pascendi", 8 Sept., 1907). The present-day legislation against heresy has lost nothing of its ancient severity; but the penalties on heretics are now only of the spiritual order; all the punishments which require the intervention of the secular arm have fallen into abeyance. Even in countries where the cleavage between the spiritual and secular powers does not amount to hostility or complete severance, the death penalty, confiscation ofgoods, imprisonment, etc., are no longer inflicted on heretics. The spiritual penalties are of two kinds: latae and ferendae sententiae. The former are incurred by the mere fact of heresy, no judicial sentence being required; the latter are inflicted after trial by an ecclesiastical court, or by a bishop acting ex informata conscientia, that is, on his own certain knowledge, and dispensing with the usual procedure
In 1192 bishop Otto of Toul ordered all Waldenses to be delivered up in chains to the episcopal tribunal. In 1194 Alphonso II of Aragon ordered their banishment from his dominion and forbade them shelter or food. The Council of Genoa (1197) affirmed these provisions and ordered death by burning against the Church.
https://www.newadvent.org/cathen/06796a.htm (3rd paragraph from the bottom)
Gregory IX was very severe towards heretics, who in those times were universally looked upon as traitors and punished accordingly. Upon the request of King Louis IX of France, he sent Cardinal Romanus as legate to assist the king in his crusade against the Albigenses. At the synod which the papal legate convened at Toulouse in November, 1229, it was decreed that all heretics and their abettors should be delivered to the nobles and magistrates for their due punishment, which, in case of obstinacy, was usually death. When in 1224 Frederick II ordered that heretics in Lombardy should be burnt at the stake, Gregory IX, who was then papal legate for Lombardy, approved and published the imperial law. During his enforced absence from Rome (1228-1231) the heretics remained unmolested and became very numerous in the city. In February, 1231, therefore, the pope enacted a law for Rome that heretics condemned by an ecclesiastical court should be delivered to the secular power to receive their "due punishment". This "due punishment" was death by fire for the obstinate and imprisonment for life for the penitent. In pursuance of this law a number of Patarini were arrested in Rome in 1231, the obstinate were burned at the stake, the others were imprisoned in theBenedictine monasteries of Monte Cassino and Cava (Ryccardus de S. Germano, ad annum 1231, in Mon. Germ. SS., XIX, 363).It must not be thought, however, that Gregory IX dealt more severely with heretics than other rulers did. Death by fire was the common punishment for heretics and traitors in those times. Up to the time of Gregory IX, the duty of searching out heretics belonged to the bishops in their respective dioceses. The so-called Monastic Inquisition was established by Gregory IX, who in his Bulls of 13, 20, and 22 April, 1233, appointed the Dominicans as the official inquisitors for all dioceses of France (Ripoil and Bremond, "Bullarium Ordinia Fratrum Praedicatorum", Rome, 1729, I, 47).