Krishna is the vishaya vigraha, that means he is the supreme object of love. Sri Radha is asraya vigraha, the supreme abode of love – the supreme lover. Every living being is the part and parcel of Krishna and similarly the inherit potential, the essence of every soul is prema – to love Krishna. All love for Krishna, within everyone, is part and parcel of Sri Radha’s love.
Krishna tells that he is conquered by the love of his devotee. Why is he conquered by each and every devotee who loves him with pure love? Because that love is a particle of Sri Radha’s love. She is the complete whole, the absolute abode of all love. Compassion is the manifestation of that love within this creation. Sri Radha is karuna mayi, she is the complete fullness, the source, the reservoir of all compassion. Sri Radha is the absolute truth.
Krishna expands himself in these two forms for the sake of pastimes of pure love. Just as Krishna is the source of all incarnations, Narayana, Dwarkadish, etc. Similarly Sri Radha is the original sources of all the queens of Dwarka, the goddesses of fortune of Vaikuntha. She is the original spiritual energy that gives pleasure to Krishna and the source of all shaktis of all the divine energies of the Lord that manifest everything that exists in all material and spiritual worlds.
What is the nature of that love? The love of the gopis is absolutlely free of any tinge of selfishness, ignorance of ego. Everything is exclusively for the pleasure of Krishna. – Radhanath Swami