Here is Thomas Watson, from "The Art of Divine Contentment":
"[This doctrine] shows how a Christian may come to lead a comfortable life, even a heaven upon earth, be the times what they will: by Christian content-ment. The comfort of life does not depend on having much. It is Christ’s max-im, ‘a man’s life consists not in the abundance of the things which he posses-ses,' (Lk. 12:15)—but it is in being contented. . . . Contentment lies within a person, in the heart; and the way to be comfortable, is not by having our barns filled, but our minds quiet. The contented person, says Seneca, is the happy man.