Brahman cannot be expressed in words. This is because you are it. Everything that appears concretely and discretely to the mind and senses is not it. That is the difficulty with truth.

The word brahman comes from the Sanskrit root bṛh and means growth, increase, increase, wide, great. But we should not take this literally, at most in the sense of infinity, boundlessness. There is neither beginning nor end to it. No one knows what it is. It is in itself inexpressible. If we write or talk about it, it is to understand that you are it, without having to do anything for it. Here the essential addition is that every idea or image that the mind forms of it, is not it.

The Upaniṣads tell us that it is boundless, beginningless and endless. This is important because we know that we exist and are conscious, but we do not know that we are existence itself and consciousness itself, in its single infinity. But brahman is not infinite space. That is another category, such a concept that arises in the mind. It is also not emptiness. Again, it is the only thing that is, the full existence. What it is, we do not need to know, and we cannot know. That we are it may nevertheless be evidently known. The key to this is already self-evident. I exist and I am conscious, hence what brahman refers to is the same as what the word ātman (self) refers to.

It is that which is infinite, and therefore even has the possibility of having an unmanifested power within itself called māyā, which imagines a world with living beings according to karmic laws. Yet brahman is pure and attributeless. This knowing and living is freedom.

Once you see that it is perfectly logical that there is only existence, and no non-existence, and that brahman never really changes into anything (so there are no real effects as the brahma kārya vādaḥ claims, kārya means effect), everything becomes clear.

Why is there only brahman and are we? Again, I cannot deny that I exist. My consciousness is. We cannot deny that brahman is existence. The only proof that there is existence is that I exist. We need the logic of a means of knowledge like vedānta to tell us that this is the only existence.

In reality there is no other. The so-called other is also just brahman-consciousness that is given a life in exactly the same way. After all, being conscious of something is the same for everyone. Why the persons differ and why they are not real and not unreal is a nuanced question for which the subjects, mithyā and karma can be studied.

The best answer to the question why a world appears, or 'why māyā?', is first of all what I just wrote. Brahman is infinite, so it can manifest itself with ease, without changing even a grain of its own reality. Hence, every phenomenon passes away. The fact that there is only brahman means that there is nothing outside brahman, nothing really created in brahman. How can anything exist outside infinity? This knowledge is an invitation to resignation and freedom.

What then is the dynamic that keeps māyā, saṁsāra going? This is the individual ignorance of living beings (jīvas, who are in fact nothing but brahman itself), because of which they keep asking īśvara (brahman with apparent qualities, saguṇa) for results with their will, fear, desire and action.

The word brahman implies the limitlessness of absolute reality, while the word ātman implies the omnipresence of reality. Everything that is I see is also as ātman brahman, non-dual.

It is important to realize that these are just words. Brahman is synonymous with consciousness. Brahman consciousness is that which accommodates the ideas that we let pass through us here. There is a direct subjective first hand (aparokṣa), that is real. But all objects of experience are not really what they seem to be, but also just brahman, the pure light of consciousness, which is therefore you yourself. Brahman is pure, without qualities (nirguṇa). It is infinite pure knowledge (jñapti, śuddha caitanyam) and therefore unprecedented in its apparent possibilities.

With infinitely great we should therefore not think in relative cosmic terms. It may be known that it is infinite in its apparent possibilities, without being a speck of non-Brahman. It can therefore make everything appear, without itself becoming anything. Unchangeable, therefore.

With that, the mathematical riddle of infinity or limitlessness is also solved in the Vedas. Infinity can be infinite, because it is non-dual. This non-duality indicates that it is unique. So there is no nothing only but the full all. And all that in simplicity. Brahman can imagine multiplicity in infinite simplicity.

Brahman is everything that there is, and yet it is simple. One, in reality nothing happens, and brahman is, very ordinary. That is me. Ahaṃ brahmāsmi, 'I am Brahman' (Bṛhadāraṇyaka Upaniṣad 1.4.10).

Nice to mention: The Sanskrit root bṛh that returns in the word bṛhat means 'great', just like Brahman in the meaning: the greatest of the great, what makes great to great'. Bṛhadāraṇyaka means great (bṛhat) forest (āraṇyaka). Referring to the forests where the seers retreated in ancient times. The space of nature thus accommodated the spaciousness in their minds, to understand the truth of brahman.

The context determines whether the term brahman refers to saguṇa brahman, brahman with qualities, or to nirguṇa brahman, brahman without qualities or properties.

There is nothing outside brahman, therefore brahman is non-dual. The potentiality in brahman for manifestation is called māyā, also a word. When māyā comes into apparent operation, it is called īśvara, god (saguṇa brahman, brahman with qualities). Only vedānta defines god so precisely. Then brahman apparently takes on qualities. Brahman is also called god, in principle it does not matter what you call it, the nuances only have to be understood. Brahman remains the divisionless, always available, unmanifested reality behind and beyond all manifestation. So we do not have to be afraid that we are no longer brahman after the death of the body.

We should not confuse brahman with brahmā, the concept of the creator god, which as a word and as an appearance is a derivative of brahman. Brahmā is the aspect of īśvara, which makes a world appear. Brahmā is also sometimes called the first teacher to understand brahman. It requires some flexibility of mind.

The satya-mithyā lesson has to be understood to understand that brahmā is brahman, but brahman is not brahmā. See there.

Brahman is sādhāraṇa, general and ordinary. It is simply the truth because it is infinitely normal. Why normal? Reality knows no distinction. The truth is the same truth for everyone. Everyone simply exists. And everyone is simply conscious. Why are dead things like a dead body or a stone not conscious themselves? This is because it lacks a subtle body, that is all.

And whether you are spiritual or a materialist, brahman is the substrate of all spiritual ideas and of matter (energy). Simple, ordinary, sādhāraṇa. So enlightenment is not something special at all. Everything and everyone is brahman. You know it or you don't know it.

If brahman is the existence-consciousness itself, we call brahman spirituality itself for all I care. But then with the sharp insight that there is nothing else than spirituality. But actually there is no point in talking about spirituality like that, because then the mind will think that you have to go to brahman or something.

Let us make it exact and precise as in vedānta. Brahman is the only conscious being, consciousness itself, existence itself, being. And (with self-mockery): that says far too much. The invitation is simply to be brahman, in all its simplicity. This simplicity is therefore infinitely simple, and that is precisely what makes it so difficult.