The triune nature of God is a very old concept; much older than Christianity. In the Norse religion, it was three God-brothers who gave life to two trees. In making the trees human, Odin gave the Breath of Life, Vili/Hoenir gave the gift of mind and will, and Ve/Lodhur/Loki gave the gift of appearance, blood, the five senses, and sexuality.
The triune concept is also found within the three children of Loki – Hela, Fenris, and Jormundgand. These children, although described as “monstrous” by Snorri in the Eddas, are also very special. They along with Loki serve to point out the fallacies of human beings.
Finally the triune concept is also found with the three Norns, the Norse Goddesses who weave Wyrd and Orlog (ur-law), the Norse version of karma, fate, and destiny. Urd is the Norn of the past, Verdhandi is the Norn of the present, and Skuld is the Norn of the future.
These three sets of three interact through the Valknut in a reciprocal flow of being. I have much more to say in the book I am currently working on about Yggdrasil. These three sets of three actually correspond to the way energy flows in the multiverse with Odin, Hoenir, and Loki representing the triad of creation, Hela, Fenris, and Jormundgand representing the triad of destruction, and the Norns the triad of being, something Thomas Carlsson hints at in his book The Night Side of the Runes. I found that the Valknut also corresponds to Gurdjieff’s Enneagram, but that is for later.