To understand what happens at death, let us first understand what death is. Death is like a bend in a continuous river of becoming. It appears that death is the end of a process of becoming, and certainly it may be so in the case of an arahant (a fully liberated being) or a Buddha; but with an ordinary person this flow of becoming continues even after death. Death puts an end to the activities of one life, and the very next moment starts the play of a new life. On the one side is the last moment of this life and on the other side is the first moment of the next life. It is as though the sun rises as soon as it sets with no interval of darkness in between, or as if the moment of death is the end of one chapter in the book of becoming, and another chapter of life begins the very next moment.
Although no simile can convey the exact process, still one might say that this flow of becoming is like a train running on a track. It reaches the station of death and there, slightly decreasing speed for a moment, carries on again with the same speed. It does not stop at the station even for a moment. For one who is not an arahant, the station of death is not a terminus but a junction from where thirty-one different tracks diverge. The train, as soon as it arrives at the station, moves onto one or another of these tracks and continues. This speeding "train of becoming," fuelled by the electricity of the kammic reactions of the past, keeps on running from one station to the next, on one track or the other, a continuous journey that goes on without ceasing.
This changing of "tracks" happens automatically. As the melting of ice into water and the cooling of water to form ice happens according to laws of nature, so the transition from life to life is controlled by set laws of nature. According to these laws, the train not only changes tracks by itself, it also lays the next tracks itself. For this train of becoming the junction of death, where the change of tracks takes place, is of great importance. Here the present life is abandoned (this is called cuti-disappearance, death). The demise of the body takes place, and immediately the next life starts (a process which is called patisandhi - conception or taking up of the next birth). The moment of patisandhi is the result of the moment of death; the moment of death creates the moment of conception. Since every death moment creates the next birth moment, death is not only death, but birth as well. At this junction, life changes into death and death into birth.
Thus every life is a preparation for the next death. If someone is wise, he or she will use this life to the best advantage and prepare for a good death. The best death is the one that is the last, that is not a junction but a terminus: the death of an arahant. Here there will be no track on which the train can run further; but until such a terminus is reached, one can at least ensure that the next death gives rise to a good birth and that the terminus will be reached in due course. It all depends on us, on our own efforts. We are makers of our own future, we create our own welfare or misery as well as our own liberation.
How is it that we are the creators of the tracks that receive the onrushing train of becoming? To answer this we must understand what kamma (action) is.
As soon as one of these bhava-kammas is generated, this "railway train of becoming" gets attracted to one or the other of the thirty-one tracks at the station of death. Actually these thirty-one tracks are the thirty-one fields of existence. They are the eleven kama lokas (realms of sensuality: the four lower realms of existence, and the seven human and celestial realms); the sixteen rupa-brahma lokas (where fine material body remains), and the four arupa-brahma lokas (non-material realms, where only mind remains).
At the last moment of this life, a specific bhava-sankhara will arise. This sankhara capable of giving a new birth will get connected with the vibrations of the related realm of existence. At the moment of death the whole field of thirty-one realms is open, so it depends on which sankhara arises as to which track the train of existence runs on next. In the same way a train gets shunted onto a new track, the force of the bhava-kamma reaction provides the push to the flow of consciousness into the next existence. For example, the bhava-kamma of anger or malice, being of the nature of heat and agitation, will unite with some lower field of existence. Similarly, one with the nature of mettā (compassionate love), having peaceful and cool vibrations can only unite with some brahma-loka. This is the law of nature, and these laws are so perfectly "computerized" that there is never any flaw in the operation.
At the moment of death, generally, some intense sankhara will arise; it may be either of a wholesome nature or an unwholesome nature. For example, if one has murdered one's father or mother, or perhaps some saintly person, in this lifetime, then the memory of this episode will arise at the moment of death. Likewise if one has done some deep meditation practice, a similar state of mind will arise.
When there is no such dense bhava-kamma to arise, then a comparatively less dense kamma will arise. Whatever memory is awakened will manifest as the kamma. For example, one may remember a wholesome kamma of giving food to a saintly person, or one may remember killing someone. Reflections on such past kammas as these may arise. Otherwise, objects related to the particular kamma may arise. One may see the plate full of food that was offered as dana, or the gun that was used to kill another. These are called the kamma-nimittas (signs).
In another case, a sign or a symbol of the next life may appear. This is called gati-nimitta (departing sign). These nimmitas correspond to whichever bhava-loka the flow is being attracted towards, such as the scene of some celestial world, or perhaps of an animal world. The dying person will often experience one of these signs as a forewarning, just as the train's headlight illuminates the track ahead. The vibrations of these nimittas are identical to the vibrations of the plane of existence of the next birth.
A good Vipassana meditator has the capacity to avoid the tracks leading to the lower realms of existence. He clearly understands the laws of nature, and practises to keep himself ready for death at all times. If he has reached an advanced age, there is all the more reason to remain aware every moment. What preparations are undertaken? One practises Vipassana, remaining equanimous to whatever sensations arise on the body and thereby breaking the habit pattern of reacting to the unpleasant sensations. Thus the mind, which is usually generating new unwholesome sankharas, develops a new habit of remaining equanimous. Very often at the time of death, if there are no very heavy sankharas to arise, habitual reactions occur; and as the new sankhara is being made, an old one from the storehouse might get stirred up onto the surface, gaining in strength as it arises.
At the approach of death, it is very likely that one will experience very unpleasant sensations. Old age, disease and death are dukkha (misery). They produce unpleasant sensations of a grosser type. If one is not skilful in observing these sensations with equanimity, then one will be likely to react with feelings of anger, irritation, maybe malice, which provides an opportunity for a bhava-sankhara of like vibration to arise. However, as in the cases of some well developed meditators, one can work to avoid reacting to these immensely painful sensations by maintaining equanimity at the time of death. Then, even those related bhava-sankharas lying deep in the bhavanga (seat of birth-producing kamma) will not have an opportunity to arise. An ordinary person will usually remain apprehensive, even terror-stricken at the approach of death and thus will give occasion for a fearful bhava-sankhara to surface. In the same way, grief, sorrow, depression, and other feelings may arise at the thought of separation from loved ones, and the related sankhara will come up and dominate the mind.
A Vipassana meditator, by observing all his or her sensations with equanimity, weakens the sankhara and thus does not allow it to arise at the time of death. The real preparation for death is this: developing a habit pattern of repeatedly observing the sensations manifesting in the body and mind with equanimity and with the understanding of anicca.
At the time of death, this strong habit of equanimity will automatically appear and the train of existence will link up with a track on which it will be possible to practise Vipassana in the new life. In this way, one saves oneself from birth in a lower realm and attains one of the higher realms, which is very important because Vipassana cannot be practised in the lower realms.
A meditator who is on the point of death is fortunate to have close relatives or friends nearby who can help maintain a good Dhamma atmosphere, free from lamenting and gloom; people who can practise Vipassana and generate vibrations of mettā, which are most favourable for a peaceful death.
At times a non-meditator will attain a favourable rebirth at the time of death due to the manifestation of wholesome bhava-sankharas such as generosity, morality and other strong wholesome qualities. But the special achievement of an established Vipassana meditator is that he enables himself to attain an existence where he can continue to practise Vipassana. In this way, by slowly decreasing the stock of accumulated bhava-sankharas stored in the bhavanga of his flow of consciousness, one shortens one's journey of becoming and reaches the goal sooner.
One comes into contact with the Dhamma in this life because of great merits one has performed in the past. Make this human life successful by practising Vipassana. Then whenever death comes, it will come with the experience of an equanimous mind, bringing with it well-being for the future.
N.B.: The analogy of a running train changing tracks should not be mistaken for transmigration, as no entity goes from one life to the next. Nothing passes to the next life except the force of the accumulated kamma sankharas.