Kṛṣṇa says that the sensory experiences, mātrā-sparśhaḥ are all temporary. Feelings of hot and cold, śītoṣṇa, sweet and sour, wet and dry, experiences of pain and pleasure, sukha-duḥkha, as well as other experiences of like and dislike are all temporary, anityāḥ. These experiences do not affect the centered person who is qualified to be enlightened, so amṛtatvāya kalpate.

These sensory experiences are anitya or impermanent and unreal. Moreover, they are relative. What may be considered hot by one person may not be perceived as hot by another.

There are many sādhus or ascetics, who stay in the higher reaches of the Himalayan mountains with least clothing; in temperatures everyone would consider bitter cold. There are those who carry out the parikramā, circumambulation, of Mount Kailaśa and Lake Mansarovar. Studies conducted on Tibetan Lamas in their high altitude snow-covered monasteries show how the Lamas can bear extreme cold without any discomfort. Renowned scientists from reputed institutions such as the Harvard Medical School have conducted such studies. When Nature is accepted totally, heat, cold, rain, dryness and all these changes do not affect the body-mind system

If we walk around without footwear, the earth that we walk upon becomes our friend. As long as we wear footwear to protect ourselves from Nature, we are treating Nature as an outsider, as an enemy. One who is firmly grounded in himself is grounded in Nature. Kṛṣṇa says that such a person is qualified and ready for enlightenment. Such persons have brought their senses under control, and as a result have their mind too under control.

What Kṛṣṇa says here, and what has been experienced by the wise sages of the East for thousands of years, is only now being grasped by scientists and researchers. It is now accepted by medical science that the body-mind dies many deaths before its final exit. Cells within our body die in thousands every day and get reborn. Over a period of a few years, every single cell in the body-mind system is replaced and renewed. What you were two or three years ago is not what you are today. Every single cell in your body-mind system, and therefore, every single bone, muscle, tissue, artery, vein, limb and body part is new, completely different from what it was two or three years ago.

The body-mind continually ceases to exist and gets recreated. It is not permanent. Separate from the body-mind system is our spirit that lives on eternally. The spirit remains the same throughout our life with no change, despite all the changes in the body-mind system. It continues to be, to exist, even after our death. The spirit does not die with the body. It lives on. It is permanent and true.

When one understands this difference between what is eternal, nitya, and what is ephemeral, anitya, one becomes a seer and knower of Truth.

Nitya and anitya do not translate into real and unreal. In the same way māyā , loosely translated as illusion, is not unreal. Māyā and anitya are real and perceived by our senses but they refer to things that are not true, that are not lasting. They are factually real but truthfully unreal! That which is true will always be true; it cannot cease to exist. Truth here refers to the state of permanence, of being eternal.

I say a living master is not present as you feel, and a dead master is not absent as you think. The presence of a dead master, an enlightened dead master, is permanent and always real. A living Master’s form is not His only presence. He is present in His absence as well.

Our perceptions through our senses may be real but not necessarily true. A dream is very real when it happens. You may get angry, frightened, excited, lustful, and such when you dream. Your body responds to these emotions and your senses react to what you observe in the dream. Yet the moment you start witnessing the dream, you awaken. You cannot dream when you become aware. The dream is not true, though it seemed real.

The same happens when you are awake and daydreaming, which is most of the time! You are awake but you fantasize. Even when you think you are fully awake, what you perceive through your senses may not be what you interpret it to mean. Your mind always filters through its own lens of the root pattern or ego. You judge whatever you perceive through your conditioned memories and then selectively put together pieces of what you perceive, to support your judgment.

source: chapter 2, Bhagavadgita Decoded