Acquire the contemplative way of seeing how all things change into one another, and constantly attend to it, and exercise thyself about this part [of philosophy]. For nothing is so much adapted to produce magnanimity.... But as to what any man shall say or think about him, or do against him, he never even thinks of it, being himself contented with these two things: with acting justly in what he now does, and being satisfied with what is now assigned to him; and he lays aside all distracting and busy pursuits, and desires nothing else than to accomplish the straight course through the law, and by accomplishing the straight course to follow God.

X, 11 - Meditations (c. 161–180 CE) - Book X