Nitya-baddhas are within this material world. Beginning from Brahmā down to a small ant, insignificant ant, they are all nitya-baddhas. Anyone who is in this material world—nitya-baddha. And nitya-siddhas, they belong to the spiritual world. They never come in contact with this material world, and even they come for some business under the order of the Supreme Lord, they do not touch these material qualities They remain always transcendental. As Kṛṣṇa remains always transcendental, even though He is in this material world, similarly, Kṛṣṇa's nitya-siddha associates, they are also transcendental. They never touch this material world.
So try to understand the position of Kṛṣṇa. Kṛṣṇa is nārāyaṇaḥ paro 'vyaktāt, transcendental, paraḥ avyaktāt. That is puruṣottama-yoga in the Bhagavad-gītā. Kṛṣṇa has said, "Anyone who has understood Me, ajam avyayam, ajam—I never take birth in this material world, neither I am deteriorated by material contact—he knows me perfectly." That is called puruṣottama.