The Bodhicaryavatara: A Guide to the Bodhisattva Way of Life
This ancient text was written in Sanskrit around 700 CE by Santideva, renowned Buddhist monk and scholar. This version is written in easy to understand language accessible to the modern reader.
If you are embarking on the path to enlightenment, or just curious, this book could be just the change agent you have been looking for. It is said to be one of the Dalai Lama's favorite texts.