Immortality is the continued existence of the human soul in a future and invisible state. 'If a man die, shall he live again?' is a question which has naturally agitated the heart and stimulated the intellectual curiosity of man, wherever he has risen above a state of barbarism, and commenced to exercise his intellect at all. The religion of all civilised peoples may be said more or less to recognise the affirmative of the question, although often under very vague and materialistic forms. Some of the most widely-spread forms of belief in the world would seem to be exceptions to this statement; for in Hinduism the goal sought is absorption into the Universal Spirit, and therefore loss of individual existence; while the pious Buddhist strives for Nirvana, or complete extinction. Yet even here the belief in a future life exists in the form of Transmigration (q.v.).
In the ancient Egyptian religion the idea of immortality first assumes a definite shape. There is a clear recognition of a dwelling-place of the dead and of a future judgment. Osiris, the beneficent god, judges the dead, and 'having weighed their heart in the scales of justice, he sends the wicked to regions of darkness, while the just are sent to dwell with the god of light.' The latter, we read on an inscription, 'found favour before the great God; they dwell in glory, where they live a heavenly life; the bodies they have quitted will for ever repose in their tombs, whilst they rejoice in the life of the supreme God.' Immortality is plainly taught, but bound up with the idea of the preservation of the body, to which the Egyptians attached great importance, as a condition of the soul's continued life; and hence they built vast tombs, and embalmed their bodies, as if to last for ever. In the Zoroastrian religion the future world, with its governing spirits, plays a prominent part. Under Ormuzd and Ahriman there are ranged regular hierarchies of spirits engaged in a perpetual conflict; and the soul passes into the kingdom of light or of darkness, over which these spirits respectively preside, according as it has lived on the earth well or ill. Whoever has lived in purity, and has not suffered the dives (evil spirits) to have any power over him, passes after death into the realms of light. In the early Greek paganism Hades, or the realms of the dead, is the emblem of gloom to the Hellenic imagination. Achilles, the ideal hero, declares that he 'would rather till the ground than live in pale Elysium.' This melancholy view of the future everywhere pervades the Homeric religion. With the progress of Hellenic thought a higher idea of the future is found to characterise both the poetry and philosophy of Greece, till, in the Platonic Socrates, the conception of immortality shines forth with impressive clearness and precision.
In the Apology and the Phædo Socrates discourses of the doctrine of the soul's immortality in language at once rich in faith and in beauty. 'The soul, the immaterial part, being of a nature so superior to the body, can it,' he asks in the Phædo, 'as soon as it is separated from the body, be dispersed into nothing, and perish? Oh, far otherwise. Rather will this be the result. If it take its departure in a state of purity, not carrying with it any clinging impurities of the body, impurities which during life it never willingly shared in, but always avoided, gathering itself into itself, and making the separation from the body its aim and study—that is, devoting itself to true philosophy, and studying how to die calmly; for this is true philosophy, is it not?—well, then, so prepared, the soul departs into that invisible region which is of its own nature, the region of the divine, the immortal, the wise, and then its lot is to be happy in a state in which it is freed from fears and wild desires, and the other evils of humanity, and spends the rest of its existence with the gods.'
It is only in Christianity, however, that this higher life is clearly revealed as a reward, not merely to the true philosopher, but to every humble and pious soul. Christ 'hath brought life and immortality to light by the gospel.' 'According to his abundant mercy, God hath begotten us again into a lively hope by the resurrection of Jesus Christ from the dead, to an inheritance incorruptible and undefiled, and that fadeth not away, reserved in heaven.' It is undoubtedly owing to Christianity that the doctrine of the soul's immortality has become a common and well-recognised truth—no mere result of speculation, nor product of priestly invention—but a light to the reason, and a guide to the conscience and conduct. For the Old Testament view see the article HELL; for other questions connected with the future state see the articles ANIMISM, APPARITIONS, CONDITIONAL IMMORTALITY, HEAVEN, ESCHATOLOGY, ORIGEN, PRE-EXISTENCE, SOUL, SPIRITUALISM, THEOSOPHY, UNIVERSALISTS; also Salmon's Christian Doctrine of Immortality (1896).