Purusha is associated with Vishnu right from core Rigveda. He is prevading Adithya who contains the universal seed/semen of creation within himself. This is supported by Rigveda itself as per Sayana
- सप्तार्धगर्भा भुवनस्य रेतो विष्णोस्तिष्ठन्ति प्रदिशा विधर्मणि । ते धीतिभिर्मनसा ते विपश्चितः परिभुवः परि भवन्ति विश्वतः ॥
- “The seven half-embryos, the seed of the universe, stand in the various directions in the cosmic order of Viṣṇu. They, through their thoughts and mind, being wise and all-encompassing, extend everywhere.”
The first interpretion of Sayana refers to Vishnu as the prevading Adithya which controls the functions of the sun . The seven embryos /entities are equated to seven rays which stand in the cosmic order of Vishnu. Those seven entities prevades the entire universe with their power and intelligence
- “Furthermore, through their understanding and intelligence, and with the intention that the world should be benefited, they encompass everything from every side. The word viśvataḥ is used in the sense of ‘from every side’. They surround and sustain the entire world; that is, they pervade the whole universe.”
- “The seven [entities] are rays, seven in number, whose nature is to move. They are ardhagarbhāḥ—those that contain water, which serves as an embryo, during half of the year. Alternatively, they exist like embryos in the middle region, within the intermediate space of the cosmic egg.
- They are the reto, the essential generative substance of the Universe, because they produce rain.
- Furthermore, through their understanding and intelligence, and with the intention that the universe should be benefited, they encompass everything from every side. The word viśvataḥ is used in the sense of ‘from every side’. They surround and sustain the entire universe; that is, they pervade the whole universe.
- Such rays stand, in their respective regions, within the cosmic activity of sustaining the world, belonging to Viṣṇu, the all-pervading Āditya (Sun).
The second half of the interpretation refers to him as the Primordial Purusha who contains the universal seed of the creation . This one is more inspired from Sankhya Philosophy.
- सप्तार्धगर्भाः सप्त महदहंकारौपञ्चतन्मात्राणीति मिलित्वा सप्तसंख्यानि तत्त्वानि
- “The seven entities are the seven principles: Mahat, Ahaṃkāra, and the five subtle elements (tanmātras).
- भुवनस्य रेतः कारणं कारणभूतानि तान्येव विष्णोर्व्याप्तस्य पुरुषस्य
- “They themselves are the causes, the causal principles of the universe, belonging to Viṣṇu, the all-pervading Puruṣa.”
Vishnu purana has a direct upabrahmana for this :CHAP. XI which explains the importance of Vishnu and his association with solar orb.
It explains the importance of seven classes of beings sustainable by Vishnu
- MAITREYA.--You have related to me, holy preceptor, the seven classes of beings who are ever present in the solar orb, and are the causes of heat and cold: you have also described to me their individual functions, sustained by the energy of Vishńu
- PARÁŚARA.--I will explain to you, Maitreya, the subject of your inquiry. The sun, though identified with the seven beings in his orb, is distinct from them as their chief. The entire and mighty energy of Vishńu, which is called the three Vedas, or Rich, Yajush, and Sáman, is that which enlightens the world, and destroys its iniquity. It is that also which, during the continuance of things, is present as Vishńu, actively engaged in the preservation of the universe, and abiding as the three Vedas within the sun.
Vishnu is associated with Purusha due to his status of one of the gods who controls the seven entities which prevades the universe and his relationship with universal seed which belongs to him.