As legate, or inquisitor, he persecuted the last Fraticelli of Ferrara, the Jesuati of Venice, the Jews of Sicily, Moldavia and Poland, and, above all, the Hussites of Germany, Hungary and Bohemia.
John's oratory was not only used to inspire religious faith but to incite mobs to conduct the mass murders of Jews in different cities in Germany. For example, 41 Jews were burned in the city of Breslau, while 36 Jews were burned in the Berlin marketplace. In addition, the entire Jewish community of Liegnitz was burned to death because of John's incitement of mobs.
Since the calendar reform following the Second Vatican Council his feast day has been returned to October 23.
He began to exert his authority by causing the churches of the Novatians to be closed and their sacred vessels to be seized.
Next he moved against the Jews and demanded that they be removed from the city. Orestes, prefect of the city, refused but Cyril led a mob of Christians against the Jews in the city, plundering and destroying the synagogues, as well as killing Orestes.
His feast day is celebrated on June 9 and, with St. Athanasius of Alexandria, on January 18.
Louis IX took very seriously his mission as "lieutenant of God on Earth," with which he had been invested when he was crowned in Rheims. Thus, in order to fulfill his duty, he conducted two crusades, and even though they were unsuccessful, they contributed to his prestige. Contemporaries would not have understood if the king of France did not lead a crusade to the Holy Land. In order to finance his first crusade Louis ordered the expulsion of all Jews engaged in usury. This action enabled Louis to confiscate the property of expelled Jews for use in his crusade.
The Congregation of the Sisters of Saint Louis is a Roman Catholic religious order founded in 1842 and named in his honour.