St. Francis de Sales' great service was to show that devotion and even high sanctity are practicable in every state of life. A perfect gentleman and a devout humanist, an apostolic man and director, he knew how to make piety lovable without taking from it the spirit of sacrifice. In the Treatise on the the Love of God contemplation is explained with the exact knowledge of a theologian and the psychology of a man who has gone through the experience.