Disclaimer: It you're completely unfamiliar with the story of Demeter & Persephone, this section won't likely mean much to you.
Each of the 4 points of a tetrahedron is equidistant from all other points. This affords us an interesting model for examining relationships in duality. Philosophy and religion have long dealt with different aspects of life in duality, such as:
Some "archetypal" subjects lend themselves to interesting analysis when their salient points are affixed to points on the tetrahedron. For an example, let's take 2 dualities and analyze them in this way.
Take Light, Shadow, Heavenly, and Earthly, and assign them to arbitrary points on the tetrahedron. Take your pick, because when you look at it, *all points are the same* in a unique way. Try it and you'll see.
So now we have 4 points:
Every tetrahedron has 6 total edges connecting the 4 points:
Let's connect these to the story of Demeter and Persephone:
Each of these represents one of the key elements in the mysterious story of Demeter. Before the 4th point (Shadow) was entered into the equation (by the capture and rape of Persephone by Hades), there was only Earthly, Heavenly, and Light. The world was in Summertime, and all was relatively well. The extra point, adding a 3rd dimension and the resulting Duality, was not a factor. Pretty blissful, eh?
Then Unity was broken by Hades' abduction of Kore. The Earth fell into the Shadow of Winter as Demeter lamented and searched for her daughter. People starved from lack of crops, and the Gods hungered from the lack of offerings that could not be made.
Demeter finally got her daughter back, but not until after Hades had managed to establish a lasting Union between himself and Persephone by getting her to eat a pomegranate seed. So she had to return to the underworld for part of each year, during which time Demeter would once again lament her loss.
During the process of all this, Demeter instituted the Mysteries to pass on the secret of broken Unity ultimately restored to a new Dualistic Unity. Neither gods nor humans inhabit the former pre-Dualistic Unity, but we now share in the Dualistic Union resulting from the entrance of the 4th point: Shadow.