You don't need to be religious to benefit from having a firm foundation for ethical living. The most eloquent, authoritative and promising of all institutions capable of informing us on ethical living is Nature.
Nature's authority for teaching us ethical living lies in this fact: As a piece of music reflects the general mood, thinking and creative method of the composer, Nature reveals the basic impulses of the Universal Creative Force. In religious terms, Nature shows us "the Will of God."
Nature is highly structured. A system of ethics can be interpreted from that structure.
For example, Nature is structured so that resources are recycled; things are not wasted. These facts amount to an ethical teaching. Nature says: It is good to recycle; it is bad to waste resources.
Nature's elaborate structure further reveals the Universal Creative Force's passion for diversity. Thus Nature teaches that humans also must cherish and hold as sacred the diverse forms and manners of being of living things.
Nature on Earth grows ever more complex as time passes. Species continually evolve toward higher, more sophisticated, more sensitive and more informed states. From that I learn that also I must constantly reassess who and what I am, and change myself to accommodate new information and new insights.
These are three of Nature's most obvious teachings. If we were to think hard we could come up with many more teachings and develop a body of "sacred literature" as impressive and much more appropriate than any gilded Bible, Koran or Torah.
However, in humanity's current early stage of evolution during which most of our behavior still is rooted in genetic programming -- matters of sex, territory and status -- embracing just the three teachings listed above make a good start.
Just these "Three Commandments" provide a sound bases for anyone who wishes to live ethically on a small, fragile Earth.