Question: Please explain what the soul is?
The soul's true existence is the Supreme Consciousness that is beyond the existence of this physical body. The basic clue is mind. Just like the sun's ray is to the sun, mind is to the Self. You see, mind itself is infinite. You cannot show the mind to somebody. There is no shape, no colour. But based on thoughts, you recognize "My mind wants to do this, my mind wants to do that." But the actual existence of the mind is consciousness. It can become conscious of any other thing also, but if you turn it backwards, if you make the mind concentrated, automatically it goes introverted and it becomes conscious of the real Self. This has to be experienced. Because it is infinite, you can not show it, or define it in any word. Just like you cannot simply define what space is and you cannot measure space by any scale. It is all-pervading. It's an amazing thing. If at all you want to measure the space and know the space, you have to become space itself.
Sri Ramakrishna used to give a beautiful example for this with His story of the salt doll. Heart realization is like a salt doll that wants to know the depth of the ocean and jumps into it. In the process, it becomes one with the ocean. The salt doll no more exists to explain. This imagined individuality vanishes, which never really existed. The real existence is of the all-pervading spirit. That is also recognized as Self or recognized as God Consciousness. This is what is achieved. This is possible only when you practice this meditation deeply. Then you will be able to experience your Self. That is how the ancient sages also determined the Self as Immortal Soul, which is beyond the birth and death of this physical body. Eternally you will always be there.