In old Finnish mythology, everyone has three souls. The souls are in fact separate spirits that inhabit the same body. One of them, henki, we are born with. It is our life force, responsible for breathing and blood flow and keeping our body warm and so on. One of the ways to say that a person is dead in present day Finnish is still, "henki lähti" - "the henki has left". It's also the root word for "breathe" - "hengittää", and "the holy spirit" - "pyhä henki". ("Pyhä", "sacred" or "holy" itself has an interesting etymology, originating from "taboo" or "forbidden".)
Then there is itse, an ancestral spirit which we acquire at the age of a few days. The word itse means "self" in modern Finnish. The ancient concept maps somewhat to "personality", which was considered strongly influenced by our ancestors. Itse is capable of separating from the person, and appearing in different locations or staying in this world after the person's death, as a ghost. Sometimes a person's itse would appear before them at a house they are on their way to visit, giving the hosts warning to prepare for the visitor. It would look just like the person, but not be real. This phenomenon was called an etiäinen.
Finally, a person's guardian spirit is called luonto. In modern day Finnish luonto means "nature". The luonto could come from the original ancestor of that person - sort of like a totem animal - or be another kind of spirit or entity, which normally lived in the spirit world or in the land of the dead, but could be raised to give the person special powers and protect them. To this day, we say that someone is "haltioissaan" - "possessed by their guardian spirit" - when a person is very excited and overcome by awe. Luonto is acquired at the time a child gets their first teeth. Children were considered extremely vulnerabe before they acquired their luonto, and in need of special protection. A person's luonto was considered to be strong if the person was very charismatic, passionate and strong-willed. There was special magic to make one's luonto stronger, if it was diagnozed to be weak by the village shaman or wizard. A strong luonto could protect a person against many ailments and curses, but posed its own risks if not balanced with the other parts of the soul.
A person could stay alive for a while if their itse or luonto left them (shamans would regularly send their itse on missions in the spirit worlds). A loss of one's itse or luonto for a longer perior was considered to be the cause for many diseases and problems. Depression was diagnozed to be a loss of the itse, "itsettömyys". Various weaknesses, like alcoholism, could result from a loss of the luonto, "luonnottomuus". These problems could be cured by summoning back the missing part of the soul and strengthening it. But a person could not survive without henki; if that spirit left, the others would leave too and the person would die.
Almost all of old Finnish medicine and magic (as well as childbirth and preparation of dead bodies) took place in the sauna. Which is something you should remember next time you enter one.
The useful observation about God was found at West Oakland Bart.