Brahman is the root source and Divine Ground of everything that exists.+

The mind is virtually the universe. The universe appears as a waking or dream (duality) and disappears as deep sleep (nonduality).  Efforts should be made to understand the mind. Advaitic is wisdom is an ancient truth preserved as a secret by sages of truth. 

                                                    

We are within the illusion. Whatever we have seen, feel, known, believed, and experienced is also within the illusion. The formless substance and witness of the illusion is the Soul of the Self.

In Self-awareness, the substance and witness are one in essence. That essence is the Soul which is present in the form of the consciousness (Spirit).      

Sage Sankara:~ 'like a servant who carries a lamp in front of you to find your way, and you have found it, so becomes the Veda to that person. What is the Veda? -- utterances of those who have known the Truth. Here is one who has known the Truth; why should he or she depend upon the Veda further? Actual realization takes you beyond books. At a certain stage, books become a botheration. The Upanishad itself says that the 'words are only so much of distraction for such minds'.

Ish Upanishads:~  Vidya and Avidya both are hindrances to Self-knowledge, but Vidya is even worse than Avidya. The word Vidya is used here in a special sense; here it means worshipping Gods and Goddesses. By worshipping Gods and Goddesses you will go after death to the world of Gods and Goddesses. But will that help you? The time you spend there is wasted because if you were not there you could have spent that time moving forward towards Self-knowledge, which is your goal. In the world of Gods and Goddesses, you cannot do that, and thus you go deeper and deeper into the darkness.

Avidya is Karma and therefore a hindrance. You perform Avidya ~i.e., you perform Agnihotra and other sacrifices. This is a roundabout way of purifying the mind, and it is also groping in the dark. But it may not have as heavy a toll on your time and energy as the other.

Ishopanishad:~ "They are steeped in ignorance and sunk into the greatest depth of misery who worships the matter, instead of the All-Pervading God and those who worship things born of matter like trees, animals, man, etc. are sunk deeper in misery."

Katha Upanishad says: ~Fools dwelling in darkness, but thinking themselves wise and erudite, go round and round, by various tortuous paths, like the blind led by the blind. (Ch II-5 P-14 Upanishads Nikhilananda)

It indicates that the ignorant one (darkness) of the Soul, the innermost Self (Atman) searches for truth by accumulating knowledge of every path and practice and is uncertain about the truth, and thinks every path leads towards reality. The ignorance of the true 'Self' leads one towards unreality or hallucination.

Bhad Upanishad:~ This Self is dearer than a son, dearer than wealth, dearer than everything else because It is innermost. If one holding the 'Self' dear were to say to a person who speaks of anything other than the Self as dear, that he, the latter, will lose what he holds dear—and the former is certainly competent to do so—it will indeed come true. One should meditate upon the Self alone as dear. He who meditates upon the Self alone as dear—what he holds dear will not perish. (8-p- -211)

It is the first instance of monism in organized religion. Vedic religion remains the only religion with this concept. To call this concept 'God' would be imprecise.  The closest interpretation of the term can be found in the books. 

Taittariya Upanishad (II.1):~ Where Brahman is described in the following manner: Satyam Jnanam Anantam Brahman - "Brahman is of the nature of truth, knowledge, and infinity". Thus, Brahman is the origin and the end of all things, material or otherwise. Brahman is the root source and Divine Ground of everything that exists and does not exist. It is defined as unknowable and Satchidananda (Truth-Consciousness-Bliss).

Since it is eternal and infinite, it comprises the only truth. The goal of Vedic religion, through the various yogas, is to realize that consciousness (Atman) is actually nothing but Brahman or God in truth.

The Soul is the Self. The Soul is present in the form of consciousness.   Consciousness pervades everything and everywhere in all three states.  The three states are nothing but an illusion created out of consciousness.  Thus, consciousness is all-pervading.

One should understand that the Soul is the cause of the form, time, and space and it itself is uncaused. The form is consciousness. Time is consciousness and space is also consciousness. Therefore, there is no second thing that exists other than consciousness. Thus, consciousness is the ultimate truth or Brahman or God in truth:~Santthosh Kumaar