Nityatva (Sanskrit: नित्यत्व) derives from nitya ('eternal, perpetual') and the suffix -tva, and means eternality or the condition of enduring without destruction of one's underlying reality.
Bhagavān's Nityatva
Śrīman Nārāyaṇa is eternal, beginningless, imperishable, and free from every intrinsic modification. His existence, knowledge, bliss, sovereignty, and auspicious qualities do not arise at any time or depend upon anything else. He alone is svatantra—absolutely independent—and remains the inner controller of all through creation, sustenance, and withdrawal.
The Eternity of Cit and Acit
Viśiṣṭādvaita does not teach that the jīvas and acit are created out of absolute non-being or eventually cease to exist. Individual selves are beginningless and retain their identity eternally. Acit too is an eternal dependent reality, though its states and forms continually change: during creation it appears with differentiated names and forms, and during pralaya it remains in a subtle causal state.
Thus Bhagavān's nityatva is unique not because He alone exists eternally, but because His eternity is independent, unconditioned, and free from the transformations and contracted states experienced by His dependent modes. A bound jīva's dharma-bhūta-jñāna may contract and later expand; prakṛti may evolve and withdraw; neither underlying reality is annihilated.
The Eternity of the Veda
The Veda is apauruṣeya and nitya: it is not the composition of a human or divine author at a historical moment. In each cycle Bhagavān reveals the eternal Vedic order again. The precise philosophical account of the eternality of words and sentences belongs to Vedānta and Mīmāṃsā discussions. The Veda is eternally authoritative and authorless, while its relation to Bhagavān's svarūpa is explained through those technical categories rather than by a simple identity statement.
Nitya-vibhūti, Nitya-sūris, and Mokṣa
Paramapadam is called nitya-vibhūti, the eternal realm. Nitya-sūris have never entered saṃsāra, while muktas have been released from it. Mokṣa is irreversible: the liberated soul remains eternally in unobstructed Bhagavad-anubhavam and kainkaryam, without losing its individual identity.