In plain words
That ‘I’ is the Ātma. So the Ātma is in every human being. It is all-pervading. But it is not seen by the eye.
Bhūtākāśa - cittākāśa - cidākāśa
In the language of Vedānta there are three: bhūtākāśa, cittākāśa and cidākāśa. What swallowed bhūtākāśa is cittākāśa; what swallowed cittākāśa is cidākāśa. The sphere of the sun is many times larger than this vast sphere of the earth with its mountains, forests, rivers and oceans. But because it is ninety million miles away from us, it looks small. And the stars are many times larger than the sun. But because they are so much farther away than the sun, they look to our eyes like tiny diamonds. Starlight travels many thousands of miles in one second. Yet the light of some stars has not reached the earth even to this day. The stars, the sun, the moon, the earth: all these are parts of bhūtākāśa. What surpasses this bhūtākāśa is cittākāśa. The earth, the sun and moon, the stars: all these are contained in the citta in a small form. You think the sun shines by its own light. But the sun receives its light from the Ātma. So the Ātma is greater than everything. This is cidākāśa. No one can describe its vastness as being like this or like that. In this world every object has a form. Every object is made up of atoms.
Since the Ātma is formless, it is subtler even than the atom. What does vision of the Ātma mean? It is to see the all-pervading principle of light. The principle of the Ātma is in every human being, in every particle. To understand this, one must go beyond form. All the objects in this world have form. But in time these forms merge in the Ātma and become formless. Man too must go beyond form and try to merge in the Ātma. All actions that have to do with form belong to bhūtākāśa.