Meditations by Marcus Aurelius. Also available via Project Gutenberg.
A Roman Emperor jots some thoughts down whilst slaughtering barbarians.
XXIV. In the ancient mystical letters of the Ephesians, there was an item, that a man should always have in his mind some one or other of the ancient worthies.
XXV. The Pythagoreans were wont betimes in the morning the first thing they did, to look up unto the heavens, to put themselves in mind of them who constantly and invariably did perform their task: as also to put themselves in mind of orderliness, or good order, and of purity, and of naked simplicity. For no star or planet hath any cover before it.