Madhudviṣa: "Those who are seers of the truth have concluded that of the nonexistent there is no endurance and of the eternal there is no cessation. Seers have concluded this by studying the nature of both." Purport: "There is no endurance of the changing body. That the body is changing every moment by the actions and reactions of different cells is admitted by modern medical science, and thus growth and old age are taking place. But the spiritual soul exists permanently, remaining the same in all changing circumstances of the body and mind. That is the difference between matter and spirit. By nature the body is ever-changing and the soul is eternal. This conclusion is established by all classes of seers of the truth, impersonalists and personalists."
Prabhupāda: This is... So far the constitution of the spirit is concerned, it is eternal. That is accepted by all philosophers, personalists and impersonalists. The only difference is that the impersonalist says that after liberation, after getting freed from this bodily contamination, the spirit soul mixes with the Supreme Soul, all-pervading, without any individual existence. Just like the same example, that the small sky within the pitcher. When the pitcher is broken, the small sky within the pitcher mixes with the big sky. The Vaiṣṇava philosopher says that the small sky is individual. It mixes with the big sky, but it keeps its individuality. The example is given in this connection: just like a green bird entering a green tree. So when the bird enters the tree, nobody can find out where is the bird because the leaves of the tree are green and the bird is also green. Nobody can trace out. But that does not mean the bird has lost its individuality. The individuality is there.