Manduka Upanishad Brahman and Atman are defined as same.+

In Manduka Upanishad Brahman and Atman are defined as same:~ सर्वं ह्येतद् ब्रह्मायमात्मा ब्रह्म सोयमात्मा चतुष्पात् / sarvam hyetad brahmaayamaatmaa brahm soyamaatmaa chatushpaat –

Manduka Upanishad, verse-2

Translation:~

Sarvam(सर्वम्)- Whole/All/Everything; hi(हि)- Really/Just/Surely/Indeed; etad(एतद्)- This here/This; brahm(ब्रह्म)- Brahm/Brahman; ayam(अयम्)- This/Here; aatmaa(आत्मा)- Atma/Atman; sah(सः)- He; ayam(अयम्)- This/Here; chatus(चतुस्)- Four/Quadruple; paat(पात्)- Step/Foot/Quarter

Fragmented Verse:~ सर्वम् हि एतद् ब्रह्म अयम् आत्मा ब्रह्म सः अयम् आत्मा चतुस पात् / sarvam hi etad brahm ayama aatmaa brahm sah ayam aatmaa chatus paat

Simple Meaning:~

All indeed is this Brahman; This Atman is Brahman; God, this Atman has four steps/quarters.

While Brahman 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. Brahman is beyond the senses, beyond the mind, beyond intelligence, beyond imagination. 

Indeed, the highest idea is that Brahman 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.

Remember:~

That alone is called the ultimate truth or Brahman, which can never be changed under any circumstances.

One must make an effort to know the ultimate truth. The Soul is the ‘Self’. The Soul is present in the form of consciousness.

Consciousness is hidden by the world in which we exist. There is nothing new to be acquired; only the seeker must be sharp enough to grasp and understand and assimilate it when told about it.

There is a difference between understanding and realization. The effort is required for this understanding, whereas once understood no special effort is needed to realize it.

Generally, people only have an idea of Soul, but once they thoroughly grasp what is the Soul they will realize the Soul is the cause of the world in which they exist and the Soul, which is present in the form of consciousness is uncaused.

Consciousness is present everywhere and in everything in the world in which they exist because the world in which they exist is nothing but an illusion created out of consciousness.

Thus, consciousness alone is the ultimate truth or Brahman. The ultimate truth is God in truth. The Soul, which is present in the form of consciousness, is God in truth.

As a lighted lamp does not need another lamp to manifest its light, the Soul, being consciousness itself, does not need another instrument to illumine itself.

The Soul regains fearlessness by realizing that it is not a Jiva (human body) but the Soul, the Self.

The world in which we exist is verily the Soul, which is present in the form of consciousness. The Soul is the cause of the universe and it itself is uncaused.

The ideas ’I’ 'me' and ‘mine’ are a reality within the dualistic illusion. The ideas ’I’ 'me' and 'mine' become quite meaningless from the ultimate standpoint.

The Soul, the innermost self is always the same in all beings and is free form, time, and space. The Soul, the ‘Self’ is formless, timeless and spaceless existence.

The Soul, which is present in the form of consciousness, is the same in waking, dream, and deep sleep.

From the standpoint of the Soul, the form, time and space are one, in essence. Thus, the form, time, and space are nothing but an illusion created out of consciousness.

Thus, the Soul, which is present in the form of consciousness alone, is real and eternal. : ~ Santthosh Kumaar