Introduction to the Devout Life

De Sales was equally known as a friend of the poor, a man of almost supernatural affability and understanding. These qualities come through in Sales' books, the most famous of which was "Introduction to the Devout Life", which - unusual for the time - was written especially for laypeople. In it he counseled charity over penance as a means of progressing in the spiritual life. Sales also left the mystical work, the "Treatise on the Love of God", and many highly valued letters of spiritual direction. He was a notably clear and gracious stylist in French, Italian and Latin. His writings on the perfections of the heart of Mary as the model of love for God influenced Jean Eudes to develop the devotion to the Hearts of Jesus and Mary.