Meditations by Marcus Aurelius
The Meditations is a philosophical potpourri of paragraphs by the Roman Emperor Marcus Aurelius (AD 121-180). The reader can see his world view thanks to recurring themes and ideas.
He believes that the world is guided by a rational principle which makes everything work out for the best. He refers to this principle as Nature or World-Nature or Providence. The way to human happiness is to act in accord with this overarching rational principle, mostly by humbly striving for the well-being of self and others. Justice is the central virtue; equanimity is the central emotional state. If someone does something against you, becoming angry or vengeful is counterproductive. It may work out for the best in spite of your immediate judgement. Even if they did commit a bad act, they probably acted out of ignorance and need pity and correction rather than scorn and retribution. We are all part of the larger community and should help each other to achieve the best for that community. The good of the community is good for all its members.
Change is constant, so expecting things to remain the same forever is contrary to the rational principle of Nature. Hardships and even death are a natural process that should not be resisted. When a person recognizes change as the fundamental principle by which Nature acts, that person accepts the course of life (long or short) granted to them and works zealously to improve the world about them. Thus they work in harmony with nature.
Marcus Aurelius's philosophy is a prime example of Stoicism, perhaps its greatest expression. Parts of it resonate with Christianity quite well, though he seems unaware of the then-fledgling religion. His emphasis on personal excellence and on forbearance in the face of evil is a model for human behavior. His idea that we should all be working together to improve mankind is also admirable if not often imitated. Some parts are less resonant with Christianity, especially how universal providence seems more like pantheism (the idea that God is in all things and all things are part of Him) than the Christian understanding of Providence.
For those interested in Stoicism or in the heights to which human reason can ascend, this is a fascinating read.