Kalyanamitra is the Sanskrit word for spiritual friendship. This friendship is something much more than someone to hang out with, but rather connotes a person or even a thing that becomes our guide, a teacher, and serves to inspire us along our path to awakening.
There is a common Zen expression that when the student is ready, the teacher appears. Ready or not, teachers are constantly appearing in our lives, but sometimes it is difficult to recognize because we are looking for someone that meets our image or idea of "teacher." Or, we regard this person or thing as an obstacle in our life, rather than as something that can awaken us to life's meaning.
For instance, we could say that illness is kalyanamitra. The death of a sibling can be kalyanamitra. The birth of our child can be kalyanamitra. Falling in love can be kalyanamitra. In short, anything which shakes us out of our ongoing slumber and creates an opening to a vista beyond our narrow image or experience of ego-self, is a spiritual friend worthy of our gratitude.
It may be difficult to regard a painful experience as a friend. We respond by pushing such experiences away or by grasping on to something else. But in zazen, we learn to sit in the midst of our suffering, much as one would do with someone in need. Just sitting. Just seeing, hearing, smelling, tasting, touching, awareness - recognizing and affirming the most essential nature of our situation, whatever it may be.
The Great Wisdom Heart Sutra is truly one of the great expressions of spiritual friendship. In this sutra, Shakyamuni Buddha expounds the truth of emptiness of all phenomena for his disciple Shariputra. He points Shariputra to prajna wisdom, the unsurpassable wisdom. Anything and anyone who points us to this wisdom is a spiritual friend. But the Heart Sutra does not stop at our own realization. It concludes with the great mantra, the vivid mantra, the unsurpassable mantra of "Gate! Gate! Paragate! Parasamgate! Bodhi svaha!" It means "gone, gone, gone beyond, together go beyond."
This "together" speaks directly to our most basic vow to save all beings. Our realization only truly comes alive when it is used in the service of others, in helping others awaken to life's essential nature. So recognize and appreciate the spiritual friends in your life: you yourself serving others in this way, and others and things continually befriending you, pointing to the unsurpassable wisdom that is our life.