The Buddhist doctrine of anatta (no self/soul) is rather mysterious from a philosophical point of view. The individual self, according to this doctrine, is best compared to a wave that is identifiable as it approaches, but at no single moment are its water molecules identical to those of a previous moment. Nothing endures after a person dies except karmic propensities; there is no individual soul or self that continues any more than a wave continues to exist. The arhat is one who has "extinguished" all desires for private fulfillment, but the question remains: Does he continue to exist? Buddhism is definitive: rebirth does not apply to him, nor does the denial of rebirth apply to him; for if rebirth applies to the arhat , anatta is false, but if not, then the arhat has been annihilated. Neither is correct, according to Buddhism.
In Buddhism, man is an aggregate of the five skandhas : body, sensations, perceptions, mental activity, and consciousness. There is no "self" underlying this aggregate, that is, no fundamental individuality. And yet the five skandhas are equally empty, according to The Heart Sutra : "this Body itself is Emptiness and Emptiness itself is this Body." The same is true for feelings, perceptions, mental formations, and consciousness. Their true nature, according to The Heart Sutra , is the nature of "no birth, no death, no being, and no non-being, ...no increasing and no decreasing". The Eighteen Realms of Phenomena (six sense organs and their sense objects, and the six consciousnesses: shape, color, sound, aroma, flavor, texture) are also not separate self entities .
In other words, the true nature of everything is nirvana or emptiness, and once we see this and are emptied of everything, nothing remains; the ego has been extinguished, and the result is the nothingness of pure joy.
I believe the best way to understand this is not from a speculative point of view, as though this doctrine arose out of a speculation akin to Greek philosophical speculation; rather, I believe it is the formulation of an interpretation of a profound spiritual experience that is common to Hindu, Jewish, Christian, and Muslim mystics alike.
In Jewish mysticism (kabbalah), silence is the condition for the prophetic state. To be silent is "to be absorbed in" (the Hebrew root of shigyonot ). Becoming fully absorbed or focused is the initial stage towards attaining the prophetic state by virtue of which one may hear and thus become a channel of God's word. To be silent is to listen; it is the posture of obedience, which, according to the etymology of the word ( obedire : to give ear to) suggests 'listening'. The successful achievement of this state is suggested by the verse from the beginning of the second chapter of Habakkuk: "O God, I have heard your hearing…" This is an interesting phrase, for he does not hear God's word, but God's hearing. It suggests a loss of a sense of "I"; for there is nothing but God. In other words, in this state, the function of hearing is nothing other than the action of God Himself; the individual has disappeared, as it were, and has become a channel of the divine. This Jewish understanding influenced Islamic mysticism; for in the Hadith ( The Sayings of Muhammad ) we read: 'I [God] become the hearing with which he hears, the seeing with which he sees, the feet with which he walks, and the hand with which he touches' (81, 38).
I believe it is this loss of the sense of 'I' that might explain the Buddhist notion of anatta , not to mention man as an aggregate at the heart of which is "nothing". I believe this Buddhist anthropology stems from a spiritual experience of that silence--after all, Buddhism is a religion first and foremost, not a philosophy; it need not literally mean there is no self, no 'I'; for the mystical state involves a loss of the ego, an emptying of the self. In Christianity, God is indeed "emptiness"; for the central doctrine of Christianity is the Incarnation of the Second Person of the Trinity, the eternal Son "Who, though he was in the form of God, did not regard equality with God something to be grasped. Rather, he emptied himself, taking the form of a slave, coming in human likeness; and found human in appearance, he humbled himself, becoming obedient to death, even death on a cross" (Phil 2, 6-8). God the Son emptied himself, for that is His nature (the divine nature), and he became obedient, revealing to us both what it means to be divine and what it means to be "man". To be fully man is to be divinized (full of grace), but to be divinized is to be "emptied" so as to be filled; moreover, to be fully man is to become obedient, that is, to listen in silence; the Son is eternally attentive to the Father, for He is the Word of the Father. The Father is that eternal silence that is unveiled by the Son. Mary herself is most fully human because she knew and embraced her "nothingness"--"the Lord has looked upon the nothingness of his handmaiden" (Lk 1, 48).
In other words, at the very depths of the human person is a 'nothingness', a non-contingent, a "no-thing", an emptiness that is fullness, a nothingness that is the most pure and perfect mode of existing, a pure activity, an eternal activity of knowledge and love. What I am suggesting is that Hindu, Buddhist, and Judeo-Christian anthropology need not be irreconcilable; they are different articulations resulting from the emphasis of different aspects of the human person. Moreover, this is why compassion has such a central place in Buddhism, because at the heart of Nirvana (in the heart of the emptiness that is God) we find our neighbor whom God loves into existence, a neighbor who also wishes to reach this state of perfect existence.
Man's true nature is this emptiness, this relinquishing of the illusory 'I', or ego. To be a human person is to "be with", that is, to be in communion with, or in community (persona: through sound, communication or community). Although man has an intellect and a will and passions (sensitive appetites), he is also alone with the non-contingent (with the Hindu Atman, the emptiness of Nirvana, with the kingdom of God that is within him (Lk 17, 21)), and it is up to the human person to choose how he is going to relate to this central core--which is emptiness, but at the same time complete fullness; nothingness, but at the same time pure existence. Will he move towards it through a gradual dying of self, an extinguishing of the ego, or will he move away from it by a life centered on the self, centered on that which is ultimately an emptiness that is not fullness, a nothingness which is nothing but nothing (egoism, selfishness, individualism)?