ANSWER: Even though God is equally present everywhere, He is not equally visible in every person or place. To explain, think of four light bulbs of 100 watts each. When turned on, each one will give the same amount of light. Then the first bulb is covered with one layer of paper, the second one with two layers, and the third one with three layers of paper, and the fourth one is left uncovered. When turned on, they will not reflect the same amount of light. And yet the same amount of light is present in each. Similarly, God is equally present everywhere, but not equally visible. He is most visible in a Divine Incarnation or a spiritually illumined soul, and the least visible in a non-living object, such as a rock.
Some anonymous ancient sages with the help of their highly evolved and transformed minds discovered this truth. Using the greatest concentration, they came to know the ultimate truth. And they called that truth Brahman.