De Sales is best known of for his spiritual classic, Introduction to the Devout Life. His teachings stand as an early example of what the Second Vatican Council would call the universal call to holiness (Lumen gentium, 5). For the most part, the laity in the 16th Century saw holiness as the role of the priests and those in religious orders. St. Francis de Sales dispelled this notion in the preface to his classic work:
But my object is to teach those who are living in towns, at court, in their own households, and whose calling obliges them to a social life, so far as externals are concerned. Such persons are apt to reject all attempt to lead a devout life under the plea of impossibility[.] (vi)St. Francis de Sales was instrumental in addressing the Calvinist movement in Europe. In addition to Introduction to the Devout Life, de Sales wrote other treatises. In particular, he wrote the Treatise on the Love of God, in which he wrote, "The measure of love is to love without measure." According to the Lives of the Saints, this was "a precept which he had consistently taught and lived" and it echoes the words of Christ: "all men will know that you are my disciples, if you have love for one another." (John 13:35)
If you would like to learn more about St. Francis de Sales check out last year's post which contains additional reading resources and an EWTN video.