The philosophy of the koshas materialized in the Taittiriya Upanishad text which dates back to the Vedic period. It is one of the earlier Upanishads written around 6th century BC consisting of three chapters focusing on understanding and knowing what is Brahman.
The third chapter of the book tells the story of Bhrigu asking his father and teacher Varuna, God of Water, what is Brahman. Varuna tells Bhrigu that Brahman is that which is born, that which continues to live and that which departs. This takes Bhrigu on a journey of exploring this answer and devoting himself to understanding what is Brahman. This results in him asking his father this question a handful of times and each time his father replies sending Bhrigu into deep contemplation where he discovers the layers of the body known as koshas and ultimately realizes that Brahman is all of these layers.
Image from healthline illustrated by Maya Chastain
The understanding of the koshas is that we are more than just our physical body. The human body is just one layer, there are four other layers which are larger than our physical selves and beyond what we can see. The five koshas, layers or sheaths, are:
Annamaya kosha is the outer most layer of our bodies and refers to the physical body. The word anna means food and this kosha is known as the food sheath. It feeds the physical body through healthy eating and regular asana practice keeping the five elements that make up the body in balance. By ensuring our annamaya kosha, physical body, is taken care of we are able to enjoy healthier bodies and experience the deeper sheaths.
Pranamaya kosha refers to the vital body which is the first subtle body layer and the bridge between the physical body and the mind. Prana means energy and this kosha is the life force sheath, also known as the vital energy layer. Pranamaya kosha relies primarily on pranayama (breathing) exercises to ensure the energy system functions optimally and the chakras are in balance. A vital pranayama kosha prevents energy from stagnating and brings the body and mind into harmony.
The manomaya kosha is the mental body and this layer represents the mind. It is where we collect information through our senses and process it. This results in our thoughts and emotions being shaped resulting in us experiencing the push and pull of negative and positive. Thoughts have a vibration and they affect our physical bodies, they affect our hormones, chemical brain balance and can cause stress or contentment. It is important to keep the mind in check by filtering the information you allow in through the practice of setting intentions, observing your thoughts and clearing the negative vibrations of the various layers of the mind by chanting mantras.
The vijnanamaya kosha is the wisdom layer. It is the wisdom that you gain from witnessing every moment. You realize you are not the body, not the mind and not the breath. It goes beyond intellect. It is no longer just mental perception or observing thoughts but an insight into your intuitive energy. It goes beyond the thinking aspect of the mind and is where you relax, practice meditation and allow your senses to dissipate.
This is the bliss body which surrounds the Atman, the inner self. This is an experience where you recognize your true nature where there is no drama, judgment but rather a sense of bliss, fearlessness and expansion. This layer allows you to see all the layers and experience an infinite expansion being part of the larger consciousness. This layer gets revealed to you once you have cultivated the other four layers. This is where you have found your true self and experience bliss that is beyond the minds ability to grasp.