At the age of twenty-five he was appointed upon the chapter of the cathedral at Osma.  Here he was conspicuous among his brethren on account of his humility, holiness, and zeal for prayer.  He spent nine years in Osma, during which time divine Providence prepared him for his important and great vocation.  This vocation became plain to him when, in the year 1204, he went to France and saw the terrible devastation which the prevailing heresies had wrought against the Church of Christ.  The sight of this disaster nearly broke his heart.  The poison of heresy had spread among the faithful with great rapidity, and principally in southern France.  From the city of Albi the heretics had assumed the name Albigenses.  These Albigenses discarded the doctrines of Christianity and constructed new doctrines that played havoc with morality and social order.  They were violent enemies of Church and State, and preached disobedience and rebellion against spiritual and temporal authority.  An enemy of the Church is invariably also an enemy of the State; history and experience prove this.

In southern France the Albigenses secured the support of Prince Raimond, of Toulouse, a wealthy and mighty, but, at the same time, a most godless and immoral prince of that time.  He had several wives; associated with heretics, and even gave his children to be educated by them.  This prince undertook the leadership of the heretical Albigenses, and with them, and other rabble by which France at that time was overrun, scoured the country, robbing and plundering wherever they went.  This lawless band, under the direction of this godless prince, robbed churches of their treasures, murdered priests, even tore open the tabernacles and desecrated the most holy Sacrament.  A messenger of Pope Innocent iii was murdered by one of these knaves, who then found the protection of this depraved prince.  Under these conditions the Pope finally saw the necessity of preaching a crusade against these heretics, who surpassed even the Saracens in the outrages committed.  A terrible war then ensued, in which these enemies of Church and State were subdued, but not converted.  For this there was necessary an extraordinary spiritual effort, and divine Providence had already prepared the instrument.  St. Dominic was the tool in the hand of God to introduce and apply an efficacious remedy, and this remedy was the rosary.

Dominic had for many years taught the doctrines of the Catholic Church to the heretics, and had converted a number of them, but not enough to satisfy his holy zeal.  He often turned with humility to God and besought Him with tears, and deeds of penance, that He might let him know how to accomplish better results.  Since childhood he had been a faithful servant of Mary, and had often said that the devotion to her was a powerful means of converting heretics and sinners.