In Manduka Upanishad Brahman and Atman are defined as the same.+

In Manduka Upanishad Brahman and Atman are defined as the same:~ All indeed is this Brahman; This Atman is Brahman; God in truth.  While Atman, which is present in the form of consciousness lies behind the sum total of the objective universe, some human minds boggle at any attempt to explain it with only the tools provided by reason. Atma is beyond the senses, beyond the mind, beyond intelligence, beyond imagination.  Indeed, the highest idea is that Atman is beyond both existence and non-existence, transcending and including time, causation, and space, and thus can never be known in the same material sense as one traditionally 'understands' a given concept or object.

If at all we said that there was a ‘Seen’ or ‘known’ substance produced at the beginning of creation, you may legitimately question us about its origin. But that has never been our argument. 

We are consistent in our assertion that there has been no legitimate cause behind anything ‘seen’ at the beginning of creation or even later on at any time. Hence there is nothing ‘seen.’ Because there has been no-thing seen, the consciousness is forever without bondage. Consciousness cannot be captured in words.

How did the “I” originate?

How did the world” originate?

How does one know that he exists in this world?

There was no cause for the universe even at the very start. So nothing was ever born. The entire universe is only an illusion. The universe in which you exist is merely an illusion created out of consciousness.

What exists is the Soul, which is present in the form of consciousness only.

Consciousness cannot be expressed in words because it is the existence itself. It is eternal, self-effulgent, and unblemished.

The illusion has no value. The universe is the illusory nature of the Soul, which is present in the form of consciousness.

Mentally reduce the universe into consciousness by realizing the universe is nothing but an illusion created out of consciousness.

There is no reason behind the illusion! From the ultimate standpoint, there is no illusion at all! Everything is nothing but consciousness.

You are still going by an attempt to establish a sequence of cause-effect relationships. There has to be a touchstone that can establish the correctness or otherwise of the sequence of causes and effects.

If we examine based on that yardstick, the causes will evaporate.

For example, doubt is a cause for a question. The cause for the doubt is ignorance. If we can get rid of ignorance, there is no scope for doubt and the later questions.

So go on finding answers to your doubts on your own. When all the questions are resolved, you will automatically land in and be at ease as consciousness. : ~Santthosh Kumaar