Sankaracarya's Vivekachudamani 567

क्षीरं क्षीरे यथा क्षिप्तं तैलं तैले जलं जले ।

संयुक्तमेकतां याति तथात्मन्यात्मविन्मुनिः ॥

kṣīraṃ kṣīre yathā kṣiptaṃ tailaṃ taile jalaṃ jale |

saṃyuktamekatāṃ yāti tathātmanyātmavinmuniḥ ||

(Sankaracarya's Vivekachudamani 567)

Just as milk poured into milk, oil into oil, and water into the water each becomes united and one, so too, one who has realized the Self becomes one with the Self.

Individual soul or Atma belongs to the Supreme Personality of Godhead. We are suffering in this world due to our separation from the source. The soul doesn't belong to the body which fills with covered bags, whiskers, nails, head hair, and body hair and filled with flesh, bones, blood, parasites, feces, mucus, bile, and air. All those are impure. We have to use this given body to reach the source, which is Sri Purushotama. Just like when we pour milk into milk and water into water. We have to go back to the creator. Otherwise, we have to suffer from repeated birth and death. One has to come to the platform of self-realization. Soul should be realise to go back to the source.