The Heart Sutra expresses the Buddha's most profound teaching, the not two-ness of all things. Because we habitually cut our selves off from the rest of existence, we resist any idea that we lack a separate self. In the Heart Sutra the Buddha tells us that all is shunyata, generally translated as emptiness. This emptiness is in fact fullness with all things.
Thich Nhat Hanh explains emptiness through a piece of paper. Where is the paper if we take away the rain, the earth, the sun, the logger who cut down the tree? Without these and many, many other conditions, the paper would not exist. It is empty of a separate self but full of all of the other things that make it up.
How does this knowledge give us comfort? While the emptiness of a piece of paper is interesting, its not particularly helpful in our daily lives. The answer is that emptiness applies to more than the material world of form.
Our mental processes are just as empty as the piece of paper. Thoughts, feelings, likes, dislikes and all other mental phenomena are likewise the result of many external conditions which are quite beyond our control or even our knowledge. The knowledge of emptiness liberates us from guilt and sorrow. We must understand, however, that emptiness does not absolve us from responsibility for our actions.
The knowledge of emptiness allows us to practice mindfulness and see how mental phenomena arise and pass away. When we see this process we become free and we see how others are overwhelmed by life because of ignorance. Our responsibility is to practice loving kindness and help others see the path to liberation.