This Self of mine within the heart, is the performer of all actions, is possessed of all good desires, is possessed of all good smells, is possessed of all good essences, pervades all this, is devoid of speech, and is without hankering. This is Brahman. ..

Here also, it is emphasized that the ‘Self’ within the heart is Brahman itself and not the soul, ‘Jiva’ or ‘Purusa’.

6.8.7:

‘That which is this subtle essence; all this has got That as the Self. That is Truth. That is the Self. Thou art That, O Svetaketu’.

This Mahavakya, Tat Tvam Asi, ‘Thou art That’ is considered one of the most important statements in the Upanishads. This statement encapsulates the whole of Vedanta philosophy, and in particular supports Advaita Vedanta.
In this statement also, we can see that only two levels of existence are defined. One is ‘thou’ or you, and the other is ‘that’, the absolute. The person is addressed directly as thou, so that thou means the person himself, in this case his individual existence. It is not said, ‘your atman (self or soul) is that’, but thou art that. Nor of course is it said, ‘you are your atman and your atman is that’.
This direct statement is one of the, if not the, greatest visionary statements, and here there is no soul defined separately. Defining a two level existence, individual consciousness and Brahman, fits in naturally with this statement while defining a separate soul would be difficult to fit in.

Kena Upanishad

1.1:

Willed by whom does the directed mind go towards its object? Being directed by whom does the vital force that precedes all, proceed? By whom is this speech willed that people utter? Who is the effulgent being who directs the eyes and the ears?

1.2:

Since He is the Ear of the ear, the Mind of the mind, the Speech of speech, the Life of life, and the Eye of the eye, therefore the intelligent ones after giving up (self identification with the senses) and renouncing the world, become immortal.

These two opening sutras of the Kena Upanishad are most important. In the first Upanishad, it is said that it is the Brahman itself which lies beyond our mind, vital force, speech, eyes and ears. No other entity like a soul is ascribed here. The complex of mind and sensations is said to be directed by Brahman itself. Here we can understand that by ‘directed’ it means supported, or brought into existence, etc. but it is important that only two levels are recognized here, the mind-sensations (including vital force), ie, the individual consciousness, and the Brahman.
The same point is emphasized again in the next sutra, He is the Mind of the mind, Speech of speech, etc. The first word, in capital letters, like Mind, Speech, etc. refers to Brahman, while the second word, mind, speech, etc. refers to our individual consciousness.
So in these first two sutras, which are considered very important sutras, a clear definition is given of two levels of existence, and an intangible entity like a ‘soul’ is clearly ruled out here.
2.4:

It is really known when It is known with (ie, known as the Self of) each state of consciousness, because thereby one gets immortality.

Here again, Brahman is defined directly as lying beyond our consciousness, with no other entity in between.

Katha Upanishad

1.2.12:

The intelligent man gives up happiness and sorrow by developing concentration of mind on the old Deity who is inscrutable, lodged inaccessibly, located in the inteleect, and seated in the midst of misery.

The important point in this context is ‘located in the intellect’, this again shows that there are two levels only, the intellect itself and the Brahman which supports it.
1.2.20:

The Self, that is subtler than the subtle and greater than the great, is lodged in the heart of every creature. A desireless man sees that glory of the Self though the serenity of the organs, and thereby he becomes free from sorrow.

Here again, the Brahman itself is said to be lodged in the heart of every creature. So there is no separate ‘soul’ entity in the heart but Brahman itself.
In the next section of the Katha Upanishad, however, there is an important description of the self which defines an individual soul, apart from the mind and the senses.
1.3.3:

Know the (individual) self as the master of the chariot, and the body as the chariot. Know the intellect as the charioteer, and the mind as verily the bridle.

1.3.4:

They call the organs the horses; the organs having been imagined as horses, (know) the objects as the roads. The discriminating people call that Self the enjoyer when It is associated with organs, and mind.

Here, undoubtedly a separate soul, separate from the mind and senses, and at the same time not Brahman, is described. The sutras go on to describe how if the horses, that is, senses are disciplined, if the charioteer is good, and so on, the master of the chariot can reach his goal and not be born again. Those where the horses are unruly, etc. are born again. So the purpose of this analogy is again to demonstrate rebirth, and hence the soul had to be described separately.
In the next section of the Upanishads, it is repeatedly asserted that this self, the soul, is non-different from Brahman. This self is ultimately Brahman itself, and the shadows that the mind throws on it do not change it in any way from Brahman.
However, even though it is asserted that the soul ultimately is the Brahman itself, this assertion does not work. Since it is born repeatedly and is trapped in the cycle of rebirth till it reaches a clear consciousness,it does have an existence apart from Brahman. Hence there are three levels of existence defined here. Although on an absolute level it may be Brahman itself, on the relative plane it does exist and it is this soul which lies in the ‘cavity of the heart’. Hence the sutras here differ from other sutras which say that it is Brahman itself which is found in the heart.
The main point here is that there is a ‘soul’ in our midst, which is the real ruler of our consciousness, and which can and does exist apart from our consciousness and can take up a different consciousness again. So when we say ‘I’, we should talk about this soul rather than our consciousness. Although the soul may ultimately be none other than the Brahman, yet when we look at it from the context of the human body, we find two levels of existence, the body-mind and the soul. This is what creates a number of logical and ontological problems.END=NAM MO SAKYAMUNI BUDDHA.( 3 TIMES ).WORLD VIETNAMESE BUDDHIST ORDER=VIETNAMESE BUDDHIST NUN=GOLDEN LOTUS MONASTERY=THE EIGHTFOLD PATH.THICH CHAN TANH.THE MIND OF ENLIGHTMENT.AUSTRALIA,SYDNEY.7/1/2015.