52 But We too hope to say something worthwhile in this matter by showing the principal reason why the holy Cure of Ars, who, as befits a hero, was most careful in fulfilling his priestly duties, really deserves to be proposed to those who have the care of souls as a model of outstanding virtue and to be honored by them as their heavenly patron. If it is obviously true that a priest receives his priesthood so as to serve at the altar and that he enters upon this office by offering the Eucharistic Sacrifice, then it is equally true that for as long as he lives as God's minister, the Eucharistic Sacrifice will be the source and origin of the holiness that he attains and of the apostolic activity to which he devotes himself. All of these things came to pass in the fullest possible way in the case of St. John Vianney.
Source: Sacerdotii Nostri Primordia (Vatican.va)