Chris­ti­an theo­logy uses a del­ic­ate term for the com­ing of Jesus into the world: incarn­a­tio, that is, embod­i­ment, accord­ing to which the divine logos took on human nature from Mary and appeared on earth as the God-man. If Jesus' being was not changed by his depar­ture, then his arrival can­not have meant an essen­tial change either – that is, he exis­ted even before his earthly birth. Ori­gen exten­ded this idea to ordin­ary souls. The doc­trine of preaex­ist­en­tia, or pre­vi­ous life, goes back to Plato, who held that at the cre­ation of the world God cre­ated souls as well, and at human birth unites them with bod­ily forms. Accord­ing to Kant, the immor­tal soul that dwells in man must of neces­sity exist before its bod­ily exist­ence too, for only that can be end­less (that is, ever­last­ing) which has no begin­ning either.

Such etern­al exist­ence of the soul – as against the tran­si­ence of the body – is self-evid­ent in the East­ern teach­ings. The ant­ag­on­ism between the etern­al sub­stance (the soul) and the tran­si­ent form (the body) is resolved by the doc­trine of the wan­der­ing of souls.

The soul's pas­sage is called transan­im­a­tion – here the emphas­is is on the anim­us, the soul, where­as in trans­mi­gra­tion what counts is the move, the change of body. The former concept focuses on the etern­al sub­ject, while the lat­ter is action-ori­ented, centred on the event that takes place. The wan­der­ing of souls (let us keep to this term) states in gen­er­al that at the death of the tran­si­ent body the abid­ing soul moves out of it into a new bod­ily form. Its con­di­tions and fur­ther details are explained dif­fer­ently by the vari­ous schools.

There are explan­a­tions – cer­tain cur­rents of Buddhism, for example, or pop­u­lar eso­ter­i­cism – accord­ing to which the soul, hav­ing cast off its human body, can take on only a human form again, and after a few incarn­a­tions the road runs straight to com­plete puri­fic­a­tion. Accord­ing to other explan­a­tions – such as the anim­ist or totem cults, or what is per­haps the old­est, the ancient Indi­an the­ory of the wan­der­ing of souls – the soul's path may also lead from a human body into other, lower forms of exist­ence. Human exist­ence is regarded by prac­tic­ally every spir­itu­al school as a priv­ileged oppor­tun­ity, in which the soul's aware­ness can mani­fest at a high level, and for this very reas­on man is answer­able for his deeds. That is, the sys­tem by which deeds bear their con­sequences, the law of karma, determ­ines the man­ner in which the body is changed.

Accord­ing to ancient Indi­an philo­sophy the soul can­not be iden­ti­fied merely with the world of the emo­tions or with the worldly per­son­al­ity, but is a spir­itu­al, tran­scend­ent­al spark of energy whose nature is being, con­scious­ness and bliss. The sub­ject of these qual­it­ies is the indi­vidu­al soul, for which the exceed­ingly pre­cise Sanskrit lan­guage uses sev­er­al terms. The term Brah­man comes from the root √bri, which means: to grow, to spring forth, to stream, to over­flow. Brah­man can mean the World Soul, from which everything comes, but also the indi­vidu­al soul, which stands in etern­al rela­tion with its source, the World Soul, like the spark and the blaze. The word Brah­man, as vital­ity, exist­ence, alive­ness, points to the soul's first trait: its being.

The term atman points to the essence, the mar­row of a thing, and so in a meta­phys­ic­al con­text it means, as against what is sec­ond­ary, what is primary, what is essen­tial. Applied to the human phe­nomen­on, this is, in con­trast to the tran­si­ent body, the abid­ing spir­itu­al sub­stance. Sub­stance, in turn, is that of which many things can be pre­dic­ated, but sub­stance itself can­not be pre­dic­ated of any­thing. Atman, then, is man's inner­most being, his very self, the bear­er of aware­ness.

Finally, the term jiva means liv­ing being, and refers to the actu­al full­ness of life, to being alive, as opposed to dead, inor­gan­ic mat­ter. This vital (Brah­man), con­scious-in-essence (atman) liv­ing being (jiva) is the etern­al entity which, after tak­ing on a body, pos­sesses that organ­ism, and which, after leav­ing the body, takes on anoth­er bod­ily form.