In basic terms, a sutra is a narrative text generally regarded as a discourse of the Buddha.
The Diamond Cutter Sutra, in particular, is one of the Perfection of Wisdom sutras, and teaches followers that although they "may aspire to attainment enlightenment in order to benefit others, [they] must question whether there exists an actual self that can become enlightened.
The very name Diamond Cutter Sutra refers to the fact that the heart of the text - honing the ability to realize the illusory nature of daily life - is a wisdom that cuts through misconceptions like a diamond. As the Dalai Lama emphasized over and over again, the root of human suffering is being in a state of fundamental ignorance, of having a false sense of self. To attain freedom, we must all cultivate insight into ourselves and rid ourselves of our distorted states of mind. We must also beware the danger of "extreme self-centeredness," and cherish others' welfare as much as our own, although our compassion for others must also be tempered by our knowledge of "not being."