St. Thomas Aquinas (1225-1274), one of the most important figures in Roman Catholicism, is honored today by the Catholic Church: it's his Feast Day.
Many books have been written about him, and the many books authored by him have been analyzed and dissected by the greatest minds in and out of the Church. To select a single quote of his would be unfair to the many famous quotes attributed to him, so herewith a number of my favorites:
Happiness is secured through virtue; it is a good attained by man's own will.Three things are necessary for the salvation of man: to know what he ought to believe; to know what he ought to desire; and to know what he ought to do.Friendship is the source of the greatest pleasures, and without friends even the most agreeable pursuits become tedious.There is nothing on this earth more to be prized than true friendship.To love is to will the good of another.