The true roots of matter are on high, close to God. They are the four holy living creatures, the Seraphim.

This means that matter is of divine origin, but at this degree of purity and subtlety, it is unknowable and inconceivable, for it is one with the spirit.
However, since discoveries in physics are revealing ever-subtler forms of matter, perhaps physicists will eventually develop instruments capable of observing the structure and movements of etheric matter.

As for astral and mental matter, it is of course unthinkable; we can only work with them. In fact, we do work with them; you all work with them, but unconsciously.

Your thoughts, feelings and states of consciousness are all material processes, but they are so subtle that their projections, the material movements they produce remain imperceptible.

Omraam Mikhaël Aïvanhov