To me the trinity involves two counterbalancing forces with a third force nudging the equilibrium just enough to set off motion and evolution. Like a guitar string has two ends pulling it taut, but the third element being a pluck is what evokes sound. Or, STO and STS spanning the spectrum of individualized evolution, with freewill manifesting from this static spectrum a dynamic sequence of personal learning experiences. Or, two ideas that seem to oppose each other, with the truth not being found between them so much as beyond them - taking a leap of cognition to transcend rather than blend this dichotomy.
Another trinity consists of active, passive, and neutralizing forces. These are compared to the fire, flour, and water needed to make bread. Fire can turn flour into bread only under the neutralizing or balancing influence of water mixed into the flour. Likewise, it seems spirit can only penetrate into lower consciousness under the neutralizing or balancing influence of freewill choice.
I'm sure there are more meanings to the trinity. John Keely wrote quite bit about the role of the trinity in his work on sound. Another one is the trinity of function, substance, and form.
What ties all the trinities together is that they encompass a perfectly balanced set of principles, where the balance is one of motion/creation rather than stillness. It takes two counterforces to produce a still tension, but a third to set this into motion. If the third is correctly proportioned and directed, the resulting motion is in itself balanced. Like adding just enough water to flour to produce edible bread.
That's as far as I understand the trinity.
Acquiring fringe knowledge is like digging for diamonds in a mine field.
