Absolute non-dualism (Advaita) is almost impossible without logical reasoning. How advaita can be reasoned out? Kena Upaniṣad (I.4) says,
त्वं विद्धि नेदं यदिदमुपासते॥ tvaṁ viddhi nedaṁ yadidamupāsate ||
It means that the concept of worship through senses should go. Brahman can be approached only through mind. Therefore, Brahman is not an object as all objects are connected to jñānendriya-s or organs of perception. After renouncing worship, which is described as dualistic in nature, one has to investigate the Self. Māṇḍūkya Upaniṣad says that everything is Brahman. But, there is subtle difference between Cosmic Self and the individual self.
Cosmic Self is space (आकाशवत् आत्मा ākāśavat ātmā), which is infinite and all pervading. It has no limitation. But the individual self is bound. In other words, when the Cosmic Self is bound, it becomes individual self. Māṇḍūkya Upaniṣad compares this to a pot. Pot is our body. Pot one day will break. But the space within the pot will not decompose. The shape of the body is the limitation factor, like shape of the pot. Irrespective of the shape of the pot, the Cosmic Self is the same. The space inside the pot and outside the pot is the same. In other words, the pot (human body) is superimposed on the Cosmic Self. Why it is so? Because, Cosmic Self is neither born nor decompose. It exists all the time. It is perpetual and omnipresent. When the pot is broken, the space within the pot becomes one with the Cosmic Self. Similarly, when the body dies, the individual soul within merges into the Cosmic Self.
The pain and pleasure of our lives are related to the body. A pot may have several blemishes like black spots, etc. No limiting factor is perfect, because they are susceptible to disintegration. Any limiting factor will have limitation of space and time. A man cannot live endlessly without death. Similarly, all limiting factors will be destroyed one day. There are several types of pots with varying ingredients like steel, wood or sand. The limiting factors will always vary. Similarly, shapes and forms of human beings vary. Some may be good and some may be bad. But the Cosmic Self is the same for everyone. It is like sun not differentiating between good and bad. For the Cosmic Self, there is nothing called good and bad. Everything is the same for the Cosmic Self, irrespective of the shapes and forms. The limiting adjuncts are nothing but the products of ignorance and illusion, which is known as māyā. Māyā is nothing but Brahman’s own power.
Māṇḍūkya Upaniṣad (III.24) says, “Brahman is without a second, but due to His Power called māyā, It appears as many; in other words, It manifests Itself in different shapes and forms through Its Power known as māyā.” We have to shed māyā, as it acts as the limiting factor and make us bound with time and space. If we look at the material world, we continue to remain bounded and transmigrate. If we try to look for the Cosmic Self within and if we are able to realize and understand difference between māyā and Brahman, then it would be easier for us to shed māyā. All we have to do is to work on our sensory organs to go past māyā. This does not mean that one has to renounce everything. What is needed to understand is the powers of sensory organs and use them in the most appropriate manner, as they directly influence the mind and cause illusion and duality (māyā).
The one who is able to control the mind from desires and attachments is able to transcend māyā by using his spiritual knowledge (buddhi or intellect; this is not mundane intellect, but a psychological term which refers to knowledge about Brahman). What happens when the mind is controlled? Māṇḍūkya Upaniṣad (III.32) says, “When the mind realizes the reality of the Cosmic Self, it stops working, as there is nothing to perceive. Further there will be no desire to perceive as the desire to perceive will not be there. This is the state of desirableness and mindlessness (amanas अमनस्) and the one who attains this state is not born again.”