What is death? The answer to this depends on one's perspective. If we think our self is our body, then death is final because it is the end of the functioning of the body, along with the conscious and unconscious mind. But this is not what Yoga, VedAnta and Tantra tell us. Again, the sAdhaka can take these as provisional truths and verify their accuracy through direct experience.
SwAmi RAma expresses the essential truths from Yoga, VedAnta and Tantra succinctly by classifying the self into three parts: the mortal self that consists of the body along with the conscious and unconscious mind; the semi-mortal self that consists of the storehouse of deep impressions created by our desires (our samskAra-s) and our individuated consciousness; and the immortal self that consists of pure Atman alone devoid of the storehouse of latent impressions. That is the Agama for those who have not yet experienced these directly.
Now we do hear reports of out of body experiences (OBE) and near-death experiences (NDE). Clearly the Agama provides a logical explanation for these experiences. One may strengthen one's belief in the scripture by the process of inference applied to these phenomena. Through sAdhanA it is possible to develop awareness that there is a self that endures even when the body, the conscious mind, and the unconscious mind are at rest. Then we come into direct contact with our causal body (kAraNA sharIra), or what SwAmi RAma calls 'the semi-mortal self'. This consists of the storehouse of deep impressions created by our desires (our samskAra-s) and our individuated consciousness. Through the systematic practice of yoga, it is possible to verify these statements for oneself, and gain conviction in the sayings that death is a change, or a pause between two states, just as sleep is a pause between one waking state and the next. The only difference is that in death, the worn-out body is cast off and at the appropriate time a new one taken on, so that the kAraNa sharIra can return to manifestation to fulfill its unsatisfied desires. SwAmi RAma likens this very elegantly to someone leaving a fortress from the front entrance, only to return through the back door! In the Bhagavad Gita, Sri Krishna tells Arjuna "Just as a man casts off his worn-out clothes, so also the embodied self casts off the worn-out body and dons a new one." (BG)
Rebirth is a difficult concept for many to accept, especially those educated in the Western liberal tradition (regardless of their ethnicity). Probably very few people are now alive who were educated in the traditional Indian gurukula that involved systematic study of the Veda-s. But if we systematically examine our prejudices and belief systems, and pursue experiments in our inner laboratory and are honest in reporting our results, then the evidence points quite strongly to the validity of the ancient wisdom.
In the Rg Vedic hymns, Yama is the first mortal to die and in the later tradition he is regarded as the Lord of Death. It is interesting that the word Yama actually means regulation, and is the same word used for the yamas and niyamas in the Yoga SUtras. In fact this is again the mirroring of the microcosm and the macrocosm. Just as the human being regulates himself through the yamas (restraint), PrajApati (or the manifested Brahman) restrains His Manifestation of all creatures through the great Regulator Yama (see BG, where SriKrishna says he is Yama). This regulation or limitation of His Manifestation we experience as death of a body. He does it to uphold the Cosmic Dharma. So death is nothing unnatural, but it is the dharma (or natural order of things) for the body to decay and die. In our ignorance we identify with the body and fear death, but the yogi calmly accepts this transition and prepares to leave the body at the appointed hour.
The story of Yama and Yami assumes a new meaning when we understand the similarity of death to sleep. In sushupti (deep sleep) the jIva is said to rest in Brahman, although no memory of this union is left in the conscious memory. In fact, as the story of YamA and Yami goes, Yama dies (yamo vA amriyata) and Yami is inconsolable. So the Gods created Night. When we see the connection between sleep and death through yoga, the beauty of this seemingly simple Rg Vedic hymn assumes a great profundity. Night is the time for sleep and respite for all jIvas, so that they may rest again in the true nature and rejuvenate themselves for another round of manifestation and play. The only difference between sleep and death is the change of the body.
Another significant mantra that is relevant to death is the MahAmrtyunjaya mantra: Tryambakam yajAmahe, sugandhim pushtivardhanam urvArukamiva bandhanAn mrtyormukshIya mAmrtAt. In this the three-eyed one (who is the fragrant Nourisher) is invoked to sever us from bondages that bind as the cucumber is bound to a creeper, so that we may escape death. Of course, to understand the import of this mantra, one needs to consider what these bondages are, and what part of the self is going to escape death. Clearly, no human however advanced in yoga can prevent the mortal self including the body from being resorbed into the five mahAbhutas (parenthetically, the expression 'sa panchatvam gatah', he went to 'fiveness' is the expression used for death in Sanskrit). The trope of cheating death and time (kAla vanchanam) is a recurrent one in Yoga. Of course, what is meant here is that by releasing oneself from the bondages to desires, action and thought, the true nature of the Self is revealed and mis-identifications with the physical, subtle and causal body are severed, whereby one then resides in one's immortal nature. So endless chanting of the mahAmrtyunjaya mantra should not lead one to cancel those life insurance policies in haste!
Certainly we grieve for the ones who were near and dear, and who are now lost. This grief is natural, but the wisdom of the ancients gives us perspective to integrate it into our life experience and thus to make better use of the remainder of our lives. It also enables us to see that at one level the people we love are loved for the sake of what they stood for (their desires, their principles, etc), not their mere bodily manifestation (later, the import of the Upanishadic statement "It is for the sake of the Self that others are loved" may become clearer.) We also see that these same desires and principles manifest in other bodies too. Often we experience the archetypal nurturing mother principle in people other than our biological mother. To celebrate this is to not demean the tremendous sacrifice that every human mother makes in giving birth, but to rather recognize and celebrate the Divine Mother (mA shakti) as She manifests through other bodies. The same can be applied to other archetypal relationships. Eventually it may be apprehended that even the Divine Mother is an archetype and a manifestation of that Universal Principle Brahman.
The concept of rebirth in the Vedic context is useful because it leads to a hopeful viewpoint that enables us to find meaning and purpose in our lives.
So understanding the nature of death also gives us insight into the purpose of life. If after this transition our unfulfilled desires are going to make us manifest again, then does this not warrant a re-evaluation of our life in the here-now? It is also said in the scriptures that it is only in the manifestation as human form can the jIva obtain liberation from the cycle of birth and death. Therefore, birth as a human is considered a great blessing. All the great sages exhort us not to squander this opportunity, but to recognize life's true purpose.
The very nature of the world is duality: life and death, happiness and unhappiness, attraction and repulsion. There cannot be one without the other. This is why the ancients emphasized the importance of the sandhyA: the moment of transition when one goes from one attribute to its exact opposite, as interpreted in this context. It is at these transition moments that one is deeply aware of the Unity that pervades and supports this duality.