Any Hinduism philosophy talks about or contemplation discussions on Why an Immortal soul requires a Mortal body? References appreciated.
The essence of the question is why did Brahman get involved in the universe by getting into bodies and physical things.
The standard theory in the Upanishads is that Brahman was “bored”. Brahman became the multiplicity of the universe because of desire to play multiple roles and be many individuals interacting with each other, instead of a single, boring existence.
See, of course, this theory is meant for our satisfaction regarding the ideal, not that this is the literal truth. That’s because the reason for the origin of the universe is a mystery. Why is there a universe? Because Brahman is ideal and perfect and self-fulfilled in every way, and has no lack of anything, no needs to be fulfilled. So the only conclusion we can draw is that Brahman was bored and wanted to play.
This above idea is also summarized in Brahmasutra 2.1.33:
The creation of the universe is merely a sport for Brahman, just as seen in the world.
Examples from Upanishads:
Taittiriya Upanishad 2.6:
बहु स्यां प्रजायेयेति
May I become many, and have offspring
Brhadaranyaka Upanishad 1.4.3:
स वै नैव रेमे तस्मादेकाकी न रमते स द्वितीयमैच्छत्
He (being alone) did not enjoy (i.e. he was bored). This is why a lonely person does not enjoy. He desired a second (individual separate from himself)
Again, the above description is not literal truth but an allegory, a symbol, a metaphor to explain a mystery that does not have an ultimate answer.
This is how the Brahman becomes many individuals. However when the individualized Brahman becomes attached to the individuality, that is the state of ignorance or avidyā. Here again, the question of why ignorance covered the individual does not have an ultimate answer. Avidyā is an observation in individuals, and ultimate Brahman-ness of individuals is also an observation. And the ultimate non-duality of Brahman is both logically and experientially proved. That is the important point. The ‘why’ question is not answerable.
But because the individual is also Brahman-substance, it has the potential to realize its Brahman-ness and thus release itself from the individual confines of a body. This is like when an earthen pot breaks, and the air inside the pot and the air outside become continuous. The only change is the removal of the boundary of the pot. The air inside did not change in order to become the air outside. This is from the “individual” perspective.
Brahman by itself is everything, so there is no sense of confinement for Brahman. This is play or entertainment. This is from the “universal” perspective.
So in other words, if the individual realizes its Brahman-ness, then it doesn’t matter if there is a body. Being Brahman, even the bodily existence is detachedly enjoyed as a play. But the trouble comes when the individual gets attached to the body itself, and so it experiences ups and downs originating in the ups and downs of the body, and get continually sucked into the roller-coaster of the body, thus forgetting its Brahman-ness.
Vivekanand provides a concise reason for why a soul needs a body : to express itself. If soul wants to express its divinity, it should take form of a body "The Hindu religion - complete works"
But why should the soul take to itself a body? For the same reason that I take a looking-glass — to see myself. Thus, in the body, the soul is reflected. The soul is God, and every human being has a perfect divinity within himself, and each one must show his divinity sooner or later. If I am in a dark room, no amount of protestation will make it any brighter — I must light a match. Just so, no amount of grumbling and wailing will make our imperfect body more perfect. But the Vedanta teaches — call forth your soul, show your divinity
I'd like to expand it further. Soul or Aatman is only satvik form of an existence. Karma is not possible with just satvik form. Rajas and Tamas are also important. That's why, we see every entity in Hinduism (Gods, demi gods, rishis etc) in some form of body, and they are always engaged in some karma. Tamas represents the body, while rajas represents the motion. Satva controls both the form of body and its motion and commits karma in the process. Satva tattva is higher in human body form than other forms of life, that's why human body is considered good for attaining moksha or clean up your karma.
But it's not only about life forms. Sun, moon, Ganga, Himalayas all have attained a body to provide divinity to this world and universe. Without the body, their divinity is not reachable to earthen beings. (Personally I believe they are just different form of souls with body or different living beings, but I guess modern science will disagree with this view).
As you can see, body is an essential component of universal law of karma and mere Aatman or soul is not sufficient. Body is a reflection of its soul and therefore its the soul which controls the body not vice versa. Therefore, soul always trumps body in existence.