In plain words
It never changes. Vedānta describes this very Ātma as “nirguṇaṃ, nirañjanaṃ, sanātanaṃ, niketanaṃ, nitya, śuddha, buddha, mukta nirmalasvarūpiṇaṃ”. The relation among waking, dream and deep sleep is the very relation among bhūtākāśa, cittākāśa and cidākāśa.
In the dream state we can see cittākāśa. Cidākāśa belongs to deep sleep, which lies beyond dream. In that alone we attain Ānanda. In deep sleep we feel so much at ease, don't we! That is to say, Śānti itself is the chief form of cidākāśa. Bhūtākāśa is perceived directly, cittākāśa lies beyond the senses, cidākāśa is pure. The Ātma principle is free of any modification and beyond shape. Vedānta describes this very principle as “śabdabrahmamayi, carācaramayi, jyotirmayi, vāṅmayi, nityānandamayi, parātparamayi, māyāmayi, śrīmayi”.
... There is no sādhana greater than this
Jesus made many efforts to see the Ātma principle that is beyond shape. So did the Buddha. “Looking at this world made up of the seen, I am being deceived; looking at the bonds of kinship that belong to the body, I am carried away with delight. The body is impermanent; the seen does not last. ‘Yaddṛśyaṃ tannaśyaṃ’: whatever is seen will one day pass out of sight,” he came to know. He went to many great souls and listened to their teachings; he studied many books. But he found no satisfaction at all. He recognised that making right use of the five elements and the five senses God has granted is itself the path to nirvāṇa. Man today performs many sādhanas without making right use of the five senses and the five elements. All these sādhanas are simply futile. We must keep sight, hearing, speech and thoughts pure. There is no sādhana greater than this. Jesus too said this very thing.