Not only does the guru perform the work of the Buddhas and thus equal them in activity, in terms of kindness the guru surpasses them. Of all Buddhas of the past who have manifested as universal teachers, it is said that Buddha Shakyamuni is kindest to us; for it is with his teachings that we have come into contact...even though Buddha Shakyamuni is most kind of the past Buddhas, still we are unable to receive teachings from him or witness his inspiring presence.
Were all the Buddhas and lineage masters of the past to manifest before us at this very moment, we would not be able to recognize them as enlightened beings. Due to our not having a sufficiently strong karmic connection with them, they would be unable to affect us. The guru performs the great kindness of coming to us in an ordinary form which we can perceive and to which we can relate, and carries out the work of the Buddhas in our lives. The fact that a donkey like us is brought into the family of spiritual beings is purely due to the kindness of the guru. The Buddhas can only come to us through him or her. Thus if we do not respect the guru and heed his or her teachings, what hope do we have? We should meditate upon the guru's unexcelled kindness and give birth to profound appreciation.
The reason why we have been wandering unceasingly in cyclic existence since time immemorial is because we have not met a spiritual master before; or even if we have met one we did not cultivate an effective relationship with him or her. We should determine to take the opportunities afforded by our present human situation and cultivate a spiritual practice under the guidance of a master.
--from The Path to Enlightenment by H.H. the Dalai Lama, edited and translated by Glenn H. Mullin,
