Boundaries are Spiritual
If you follow any of the traditional, classic spiritual training schools, one of the foundational practices is the attempt to dissolve the personal will. To destroy the illusory ego. You'll be asked to fade the boundaries of self and dissolve into the will of the whole. In practice, this means to say yes to the teaching and the teacher and a firm 'no' to your own desires, wishes, and dreams.
You are taught a gradual process of losing the grip on your own personal boundaries while following the strict constructs of the boundaries set by someone else. The training into "spiritual boundaries" happens in stealth. It begins as an invitation to change your lifestyle and your choices. By and by, you are offered more invitations to transcend, transform, or transmute your current reality into a more "enlightened" way of being. Before you know it, your circle of self-influence, boundaries, and emotional opening have been shifted into a reality that no longer reflects your true nature and freedom of choice.
In a way, when you follow a dogma, a religion, or a defined spiritual teaching, you are given a set of dos and don'ts. A set of rules that promise a better tomorrow. The now, the present, where you are at needs to be shifted, changed, and revised in order for you to be happier, better, more pure, and eventually enlightened. The inherent flaw in this perspective is the inevitable destruction of your own sense of self, which you have built over years of refinement. You have tried and tested reacting with the world around you and built a complex set of boundaries in order to protect yourself and offer a sense of solidity when interacting with others.
Many of the spiritual traditions attack those constructs and explain that those boundaries are exactly that which hold you back from experiencing life as it is. The explanation given is usually around having those mental constructs act as colored filters between you and reality.
If we examine this closely, we might realize that, in many cases, this might be true. Our sense of defensiveness is overreacting and creates a much thicker wall between the other and us than actually needed. Yet, a complete dissolution of these boundaries is a violent act, which will be more harmful than constructive. In all of my years of spiritual development and teaching, I have seen much more destruction and pain coming out of these boundary deconstructive practices than any other abuse I've ever witnessed. The main reason for this is that, in this case, there is no perpetrator and only victims. You become your own executioner, and the sense of guilt is more than overwhelming. Once those boundaries are challenged deeply enough, it is almost impossible to restore the balance and offer self-love and acceptance back to oneself.
The sense of I and thou, the ability to discern our own preferences, liking, and inclinations, is the deeper metaphysical meaning of life. We have morphed into a dual reality from a cohesive sense of oneness. What the East calls Brahman, the state of nothingness which contains all, is the origin of this existential sense of two-ness, of the necessary sense of separation we need in order to appreciate each other, life, and ultimately the profound experience of self. Self implies other, and other implies self. These are not complimentary terms but existential implications.
We are not here to return to oneness but a sense of oneness in pursuit of experiencing itself within the duality and variety of life. That is a very profound statement because if you are willing to open to this concept, not only that your spiritual boundaries are important, they are necessary.
Your boundaries define who you are. They allow you to be you so I can be me. My boundaries allow for me to be me so you can be you. Studying compassionate communication and other non-violent communication tools allow us to express our need for healthy boundaries without overstepping someone else's need for respect or being heard.
In my years of experience, there is no better spiritual practice than investing in learning to communicate. Our external ability to converse, listen, and hear another is truly the same relationship we have with ourselves when observing our inner dialog. The difference between treating your mind as a friend or a foe can sometimes be just one communication tool away.
In summary - spiritual boundaries, the understanding of choice and freedom, and the ability to express our preferences and likings are the crucial and foundational steps to a healthy development of any spiritual aspiration. As one of my teachers, Monique Darling, says- "No is a complete sentence." You are not more developed if you can only say yes. If you do, your nos actually have no meaning. Only when you have a strong sense of self, and a strong sense of boundaries, your yes would actually be true.