Those called Shravakas see into the four Truths to obtain Nirvana of nothingness. These four Truths are said to be what is certain and without error. In the Sutra of the Last Teachings it is said: ‘The moon may become hot and the sun cold, but the four Truths taught by the Buddha will never change.’ Heaven and earth may be overturned but the principle of the four Truths will not be shaken. The four Truths stand on the doctrine of delusion, action and suffering already discussed. It comes down to this: Everything is delusion, action and pain. The present life is a result which has been incurred by delusion and action in past lives, and the doctrine of a power which brings about the result is the second Truth. The second Truth is that delusion and action in the past are, taken together, the fundamental cause of pain.
They speak of the path as the practice by which the fundamental causes have to be extinguished in order to extinguish suffering. To be free from birth-and-death, the causes (delusion and action) must be destroyed, and the appropriate practice is termed the Way, there being thirty-seven auxiliaries. Finaly, by the way of practice which destroys delusion and action, there is attained realization of Nirvana called extinction. Extinction is Nirvana. Extinction means that there is nothing. The extinction-Truth is realization of a Nirvana in which life has altogether ceased to exist. So the practice of the Shravakas is to absorb the four Truths into the mind in the expectation of becoming free from life.
To sum up, both Pratyeka Buddhas and Shravakas think that our desire and grasping are things to be done away with. If they can be completely done away with, we become like empty snail-shells. Their Nirvana is in thinking that they have completely done away with the causes of life. In that they believe they have realization.
This view, which would extinguish what is not to be extinguished, and which thinks it has been extinguished, is a shallow one; shallow indeed. Their Nirvana is an empty void, nothingness, and as such it has no meaning for life.
by Abbot Obora of the Soto Zen sect