The original unbroken lineage of enlightenment is present within the mind-streams of all sentient beings, and revealed at the time of their realization of enlightenment. Because sentient beings have the habit of dividing inner and outer, and relying on outer circumstances, an outer component to the path towards enlightenment exists.
This outward counterpart to one's original enlightened nature is the continuous transmission of the two Dharmas, that of scripture, based on wisdom speech that has been accurately transmitted over time, and that of realization, immediate in the minds and histories of sublime teachers from the earliest times up to the present day.
These two streams constitute the manifest, living wisdom lineage of the Buddha Dharma. Because enlightenment, which benefits and releases all beings including ourselves from suffering, is the highest good, the wisdom lineage of enlightenment is the present embodiment of the highest good. Based on this understanding, all Buddhist traditions support and venerate the scriptures and teachers who guide them to enlightenment, and attempt to maintain a clear account of their historical lineage, as a guarantee to themselves and future generations of the source and efficacy of their teachings.
We should understand that the basis of the Dharma is its beneficial connection with the minds of beings. As HH Dungse Thinley Norbu Rinpoche points out in his incomparable book, White Sail, "... the deepest meaning of teaching is not the form or aspect of any particular teaching, but the meeting of the teaching with the mind...." Thus, though the the wisdom lineage of the Dharma always has an unmistaken historical element, even more important to us is its embodiment in the present minds and living memories of wisdom teachers. This living lineage functions to inspire, aid, inform, instruct and guide beings on their path to enlightenment.
Regarding the supreme importance of the spiritual teacher then, as Rinpoche writes, "It is necessary for us to create an object of love through the great wisdom cynosure of sublime being's presence. Then, we can make the wonder of spiritual qualities blossom through faith, including the incomparable love of compassion."
Precious words like these show us the way to practice Buddhism. Lineage and teachers are inseparable and indispensable in its paths and practices. The more our sincere and honest practice flourishes, the more our own compassion and wisdom will reveal itself. Then, as this occurs, we ourselves can become a shining jewel, joined upon the precious rosary of wisdom lineage.