Everything in the world characterized by three dimensions, that is, everything we call a compound, is constituted by three vertical or distinct levels. Some examples may make this clear. We know from visual experience that every muscle in the human body is made up of tiny fibers and that these, gathered into bundles, make up the larger fibers we call motor fibers. From these bundles come that compound entity called a muscle.
It is the same with our nerves. The smallest fibers in them are woven together into larger ones that look like threads, and gatherings of these are woven together into nerves. It is the same with the rest of the weavings, bundlings, and gatherings that make up our organs and viscera. They are compounds of fibers and vessels in various arrangements, depending on similar levels.
It is the same as well in all the members of the plant kingdom and all the members of the mineral kingdom. There are threefold gatherings of filaments in wood and threefold conglomerates of elements in metals and rocks as well.
We can see from this what distinct levels are like, namely that one level is made from another and a third from the second, the third being called a compound. Each level is distinct from the other.
from Divine Love and Wisdom, Section 190