St. Louis’ seminary years shaped the goal of his priestly life: to be a missionary to the poor, either in France or abroad. He would later write to his spiritual director: “I had wished…to form myself for the missions and in particular for teaching catechism to the poor…I feel a great desire to make Our Lord and His Holy Mother loved, and to go about in a poor and simple way, catechizing poor country people.”
Ordained a priest at the age of 27, on June 5, 1700, Louis-Marie celebrated his first Mass in the Church of Saint-Sulpice, at the altar of the Blessed Virgin. Though St. Louis’ priestly ministry would last only 16 years, he sanctified that time by traveling alone and with different groups of missionaries around France to minister to the poor and to preach the love of God to them