Most of us are familiar with the idea that our past experiences play an important role in the formation of the beliefs we hold about ourselves, our capacity for forming love relationships, and our perception of our capabilities (e.g. developmental psychopathology).
We are also often aware that despite our best intentions and the use of 'will power' it can be very hard to disengage from self-defeating or self-indulgent behaviours and reactions that lead to results we don't really want - at least consciously (for a comprehensive account of psychological mechanisms through which persoanl agency is exercised, see Bandura, (1989)). While 'positive thinking' can sometimes be helpful, for example in affirming our self-esteem, in most cases the moment we relax our efforts, we are back where we started. Deeply held patterns have a habit of reasserting themselves.
Personal growth or development requires flexibility in our capacity for thinking and perceiving. It requires the ability to be open to new information, to be able to change contexts when appropriate, and to process multiple streams of information in flexible ways. If past experiences were not fully integrated or worked through at the time, they introduce rigidity into our system and adaptation and movement to higher levels of functioning become problematic. In other words, unintegrated aspects of our past hold us back in our development, blocking or limiting experiences like centeredness, empathy, connectedness, love and compassion.
As mentioned elsewhere on this site, integration of experience (past and present) is the most fundamental aspect of successful human development and the achievement and maintenance of wellbeing. Breathwork promotes integration and thus promotes personal growth.
Breathwork also fosters spiritual development. In fact, Breathwork is often experienced as liberating in a spiritual way. Breathwork is a meditative process that leads to transcendence of preoccupation with one's own concerns. Breathwork promotes disidentification with thoughts, feelings and emotions by establishing the ability to observe those phenomena as they are experienced and pass through consciousness without becoming attached to them. This is one of the fundamental aims of meditation practice.
Breathwork also induces an altered state of consciousness (along with dynamic flows of energy throughout the whole body) in which the experience of universal love and caring toward others and nature can be experienced.
References
Bandura, A. (1998). Human agency in social cognitive theory. American Psychologist, 44, 9, 1175-1184.