Our urge to attach metaphysical meaning to number—numerology—has had many expressions, both ancient and modern: Greek Pythagoreans, Jewish Kabbalists, Catholic Trinitarians, as well as many others.
But for the metaphysical import of certain numbers, one need look no further than the human body or the night sky.
Because we have 2 eyes, 2 ears, 2 legs, 2 hands, and 2 hemispheres in our brain, the number two has metaphysical significance. (Perhaps the preponderance of double features of our anatomy is why we have many conceptual dualisms: yin / yang, good / evil, hot / cold, love / hate.)
Because there are 3 large objects in our heavens—the sun, the earth, and the moon—the number three has metaphysical significance. (A triangle is formed from three points in space.)
But the metaphysical (and metaphorical) significance that we attach to certain numbers is culturally and historically arbitrary. Plastic.
The number three is important to Catholic Trinitarians because they believe God can be expressed as a trinity of Father, Son, and Holy Spirit. (A patriarchal expression wholly devoid of the feminine principle.)
I like to ground the importance of the number three in a simpler observation: the three most obvious objects in our sky are the sun, the earth, and the moon. And the sun came first, then the earth, and then the moon.
In both a metaphorical and literal sense, Sun, Earth, and Moon corresponds to the meme Father, Mother, Child.
And, I hypothesize, because we all are a child of a father and a mother, we naturally want to attach importance to the number three—to the number of people in the simplest family. But I have no idea how to test that hypothesis. 🙂