'dvitīya catur-vyūha' ei--turīya, viśuddha
vāsudeva-the expansion named Vāsudeva; saṅkarṣaṇa-the expansion named Saṅkarṣaṇa; pradyumna-the expansion named Pradyumna; aniruddha-the expansion named Aniruddha; dvitīya catuḥ-vyūha-the second quadruple expansion; ei-this; turīya-transcendental; viśuddha-free from all material contamination.
Vāsudeva, Saṅkarṣaṇa, Pradyumna and Aniruddha constitute this second quadruple. They are purely transcendental.
We should always remember the differences between spiritual and material actions. The Supreme Lord, being all-spiritual, can perform any act without extraneous help. In the material world, if we want to manufacture an earthen pot, we need the ingredients, a machine and also a laborer. But we should not extend this idea to the actions of the Supreme Lord, for He can create anything in a moment without that which appears necessary in our own conception. When the Lord appears as an incarnation to fulfill a particular purpose, this does not indicate that He is unable to fulfill it without appearing. He can do anything simply by His will, but by His causeless mercy He appears to be dependent upon His devotees. He appears as the son of Yaśodāmātā not because He is dependent on her care but because He accepts such a role by His causeless mercy. When He appears for the protection of His devotees, He naturally accepts trials and tribulations on their behalf.