Triads of gods appear very early, at the primitive level. The archaic triads in the religions of antiquity and of the East are too numerous to be mentioned here. Arrangement in triads is an archetype in the history of religion, which in all probability formed the basis of the Christian Trinity -
C G Jung, A Psychological Approach to the Dogma of the Trinity
It makes an enormous practical difference whether your dominant idea of totality is three or four.
Collected Works, vol 18, par 1610.
Carl Jung and the Trinitarian Self
Quodlibet Journal: Volume 4 Number 2-3, Summer 2002
The title of this article could hardly appear more oxymoronic. However, we are all driven by our own daemons and mine set me the task of uniting a firm belief in the completeness of the trinity as the foundation of the human psyche with Jung’s psychological schema.
In all mental and spiritual honesty I could not wholly abandon one or the other, so in Jungian fashion I had to employ the third term.
At the heart of the psyche Jung said duality existed, and it was the balance of opposing forces which created a normal, neuroses-free individual. But even this could not completely satisfy Jung. In 1918 whilst drawing his mandalas he discovered what he named the third term, the necessary mechanism to harmonise the forces in opposition.
He postulated that the ego performed this function, and hence gave rise to man’s psychic evolution from the animal kingdom. The Trinity was the rock on which the hope of introducing Jungian psychology wholesale into Christian theological thinking foundered, when Jung’s associate Father Victor White refused to accept the inadequacy of the Christian position.
One of the most important ramifications, unacceptable to White (and to many other Christians), of the Jungian quaternal recipe is the reinterpretation of the nature of evil and its personification in the real or mythological being of the Devil. Not only did their collaboration cease but also, sadly, did their friendship. (Full Article)