The writings of the rasik (one who has tasted Divine bliss) Saints, what we call a rasik vāṛṇī (Divine nectar-filled exposition) go beyond what is revealed in the scriptures like the Vedas, the Upanishads, the Bhagavad Gita, the Bhagwatam, and other Purāṇas.
A rasik Mahāpuruṣh is someone who has tasted the ras (Divine nectar) of Bhagwan (God). Ras is mentioned at many places in the Vedas, just like
रसो वै सः, रसं ह्येवायं लब्ध्वानन्दी भवति…।
Raso vai saḥ rasaṁ hyevāyaṁ labdhvānandī bhavati…- Taittirīya Upaniṣhad
Ras is the essence of bliss, and bliss is God. So,
आनन्दो ब्रह्मेति व्यजानात् ।
Ānando brahmeti vyajānāt.
When the Vedas say Brahm (the Absolute) is anand (bliss), Brahm is bliss and the essence of bliss is ras. Ras, in English we could say, means nectar. Just like a mango is sweet, but if you extract just the juice from that mango and concentrate it, you have the nectar of the mango. So ras is the essence of Divine bliss.
And when the Vedas say,
रसो वै सः,
Raso vai saḥ,
It means ‘God is bliss’. Shree Krishna is not just bliss; God is ras, so Shree Krishna is ras.
Ram and Krishna reveal the ras. There are other forms, Almighty forms, like Vishnu, Durga, and Shiv. They do not reveal the nectar of God’s lovingness. They reveal the bliss of God’s Divinity, but not the nectar of His lovingness.
It is like the difference between admiring the king from a distance and having the king invite you to a casual lunch, where you get to hang out with him like a buddy. It’s the same king, right, but it’s a big difference.
So Ram and Krishna allow that proximity, that relational proximity. So they reveal the ras of Bhagwan, whereas the other Almighty forms do not. So one who has tasted this ras is called a rasik. It is a certain classification of Saint. All God-realized Saints have attained the same God, but they have attained God in different ways according to how they worshiped God when they were devotees.
So some surrender to God and wish to merge into His formless aspect. These are called gyānī Mahāpuruṣh (knowledge-realized Saints) or gyānī Saints. Some worship God and wish to have that Divine vision of God in His Almighty glory, like admiring the king from a distance. They are called bhakt (devotional) Saints. But those who wish to have that relational proximity are called rasik Saints, rasik Mahāpuruṣh, because they have tasted that ras.
So those rasik Mahāpuruṣh, they have the actual experience of who Krishna is and who Radha is. So they reveal the secrets of who Radharani is in their writings.
