Oum PoorNamadah PoorNamidam

ॐ पूर्णमद: पूर्णमिदम्
(This is full, that is full)

The shloka goes:
THIS is full. THAT is full.
THIS came out of THAT.
THIS coming out of THAT, THAT remains full (as ever).

THIS refers to the soul (jeevaatmaa). THAT is the Universal Soul (paramaatmaa).
FULL means self-contained, self-conscious, eternal and immutable. THIS and THAT are one and inseparable. Otaprota (a combined SamskRuta word) - meaning all pervasive and all permeating - within and without - inside and outside - just like warp and woof of a woven cloth.

THAT means IT is here , is is far away. BUT That is here, there and everywhere! That is neuter gender. That is unmanifest and without a body, hence neither male nor female.

THIS is not a part of THAT, like the limb of a body which cannot be separated. THIS is integral with THAT like Ardhanaareeshwara.

THAT is both the sentient and material cause of the manifested universe. IF not the material source, then you have to explain WHO made the material. Another THAT? And indeed with what earlier material and WHO indeed made this earlier material and so on. Absurdity.*

NOTE:
Thou art That. YOU ARE THAT. Ramana advises -Forget for the time THAT which is not "here". Find out WHO YOU ARE . You will automatically and simultaneously know THAT beause You are already That .