I read this from the Wikipedia entry on the life of this great saint. The words of the saint, mentioned in Bl. John XXIII's encyclical are highlighted.
Sacerdotii Nostri Primordia
* his "voluntary affliction of his body" which "led him to abstain almost completely from food and from sleep, to carry out the harshest kinds of penances, and to deny himself with great strength of soul." Vianney engaged in these mortifications as penance on behalf of the sinners he ministered to: "I impose only a small penance on those who confess their sins properly; the rest I perform in their place."
* his life of poverty, "a life that was almost completely detached from the changeable, perishable goods of this world." The encyclical points out that Vianney said "My secret is easy ... give everything away and keep nothing for yourself" and that "There are many people keeping their money hidden away while many others are dying of hunger."
* his life of chastity. The encyclical points out that Vianney said "A soul adorned with the virtue of chastity cannot help loving others; for it has discovered the source and font of love—God."
* his life of obedience, living in such a way that he "burned himself up like a piece of straw being consumed on fiery coals."
* his administration of the sacrament of Penance, which Vianney took so seriously that he said: "So many crimes against God are committed that they sometimes incline us to ask God to end this world! ... You have to come to the town of Ars if you really want to learn what an infinite multitude of serious sins there are... Alas, we do not know what to do, we think that there is nothing else to do than weep and pray to God." The encyclical also notes that Vianney said: "If there were not very innocent souls to please God and make up for our offenses, how many terrible punishments we would have to suffer!" Yet, the encyclical also points out that Vianney said: "God is quicker to forgive than a mother to snatch her child from the fire."