The cardinal doctrine which they seek to teach is that souls do not die, but after death pass from one to another; and this belief, as the fear of death, is thereby cast aside, they hold to be the greatest incentive to valor.

Cæsar, C. J., “De Bello Gallico”, vi, 14

The Pythagorean doctrine prevails among them [the Gauls], teaching that the souls of men are immortal and live again for a fixed number of years inhabited in another body.

Diodorus Siculus, “Histories”, v, 28, 6

 Between them came the Druids, men of greater talent, members of the intimate fellowship of the Pythagorean faith; they were uplifted by searchings into secret and sublime things, and with grand contempt for mortal lot they professed the immortality of the soul.

Ammianus Marcellinus, xv, 9, 8

However, not only the Druids, but others as well, say that men’s souls, and also the universe are indestructible, although both fire and water at some time or other prevail over them.

Strabo, “Geographica”, iv, 4, c. 197, 4

And you, O Druids, now that the clash of battle is stilled, once more have you returned to your barbarous ceremonies and to the savage usage of your holy rites. To you alone it is given to know the truth about the gods and deities of the sky, or else you alone are ignorant of this truth. The innermost groves of far-off forests are your abodes. And it is you who say that the shades of the dead seek not the silent land of Erebus and the pale halls of Pluto; rather, you tell us that the same spirit has a body again elsewhere, and that death, if what you sing is true, is but the midpoint of long life.

Lucan , “Pharsalia”, i, 450-8

One of their dogmas has come to common knowledge, namely, that souls are eternal and that there is another life in the infernal regions, and this has been permitted manifestly because it makes the multitude readier for war. And it is for this reason too that they burn or bury with their dead, things appropriate to them in life, and that in times past they even used to defer the completion of business and the payment of debts until their arrival in another world.

Pomponius Mela, “De Situ Orbis”, iii, 2, 18 and 19

Transmigration – Passage of the soul after death to another body.
We will not get into the fine details as there are many thoughts on this. The different traditions and folks within the greater community have different details on this but the foundation is the same and that is the belief of another life after this one. As one can see from above The Senogalatis (Ancient Gauls) believed in the transmigration of the soul and, that the soul is immortal to be born again. Within Gaulish thought, this is crucial for us to understand them and the inner workings of the cosmos around us. So that being said this is one of our fundamental teachings. Life, Death, and, Rebirth is always happening around us one only has to look toward nature to see this doctrine at work.