From the introduction:
If spirituality is the negotiation of the boundaries between “I” and “we,” the purpose of breathing meditation is to clarify those boundaries. It is necessary because being born into a new life is an intensely shared experience, creating connections that make it difficult to know where we stop and another (initially mother) begins. The first goal of breathing meditation is to be confident in our sense of self.
Even as we separate life remains a collaboration. What is no longer needed by us can be a gift to other living things. What they no longer need can be a gift to us. To meditate on our breath is to be conscious of that exchange: we exhale carbon dioxide, and plants release oxygen.
To master breathing meditation is to make exchange the sole focus of our awareness. As mastery grows, awareness extends to subtle exchanges of thoughts and then pure energy. Obviously breathing meditation is not mastered in a day.