|In Old Celtic (Gaulish-Brittonic and Goidelic), the word for rebirth was ategenos (Old Irish aithghen). In this doctrine of limited reincarnation the spirit of an ancestor was reborn among his or her own kin. This means that certain inherited characteristics and even Deuoi (Tuatha Dé Danann gods) would sometimes appear or reappear in a family lineage.
More often, though, it meant that a particular deity would choose to befriend a particular lineage and incarnate him or herself within that lineage, and thus a child could be born possessing certain characteristics of that deity. The child would not necessarily embody the personality of that spirit or divinity (though this sometimes happened in the cases of great heroes), but certain attributes or talents would develop as gifts from that divinity.
Such a phenomena was interpreted as rebirth in much the same way that a mother might say that her infant son "has his father’s eyes," or a father might say that his son "has his grandmother’s talent for music." Today most people are likely to interpret these familiar family traits as genetically inherited, but this was taught by the Druids to be a form of rebirth and well-known as such in the Celtic faith. Spiritual possession was another aspect of this belief, but ategenos differed very greatly from modern-day conceptions of reincarnation and karma borrowed from theosophy and certain sects of Hinduism, which also state that people are punished for sins by paying for them in the next incarnation. The Druids never taught that people were rewarded or punished according to principles associated with the reincarnation process of karma. The Druids would have thought such ideas absurd.
The Deuoi, or higher divinities, were creative, shape-shifting spirits and could incarnate in many forms through their magic. The Deuoi were in fact manifestations of a force greater than themselves. They are capable of taking many forms or guises as well as walking the earthly realm of the manifested world. This is very probably the reason the Druids avoided representations of the Deuoi as human in art until they were conquered by the Romans. It is also why the Romans equated Lugus, like Woden, with their own Mercury (Hermes), who was considered the messenger of the Gods. Celtic gods were like the Devas of Vedic religion.