This tale occurs in the Padma Purāna (5.74.60-198). Here, Arjuna transforms into a ‘Gopi’ named ‘Arjuni’ to enjoy the Rāsa dance with Krishna. The background for such a tale can be seen in the Mahābhāratam, namely in the eternal and divine friendship between Arjuna and Krishna.
Arjuna is an incarnation of ‘Nara’ (man) and Krishna is of ‘Nārāyana’ (God). In the Bhagavad Gitā, Krishna instructs Arjuna to ‘priyā priyārharhasi Deva sodhum’ (to come to him as a lover). This is symbolic of the divine love between the Soul – Arjuna and the Supreme – Krishna.
This divine love is referenced many times in the Mahābhāratam. For instance, in the Vana Parva, Krishna says to Arjuna: ‘You are mine and I am yours, while all that is mine is yours also! He that hates you, hates me as well, and he that follows you, follows me . . . You are from me, and I am from you!, No one can understand the difference that is between us!’ Moreover, In the Sauptika Parva, Krishna states, ‘I have no dearer friend on earth than Arjuna, and there is nothing that I cannot give to him, including my wives and children.’ In the Drona Parva, Krishna reiterates, ‘I shall not be able to cast my eyes, even for a single moment, on the earth bereft of Arjuna . . . Know that Arjuna is half of my body.’
Going back to the Padma Purāna, Arjuna wishes to know about all of Krishna’s divine experiences with the Gopis in his Rāsa dance. Upon Arjuna’s persistence, Krishna instructs Arjuna to bathe in a sacred lake, which changes one’s gender. Upon bathing, Arjuna becomes a beautiful and youthful maiden named Arjuni, resembling the women of the cowherds (Gopis).
Krishna attracted both men and women due to this divine charisma. Upon seeing Krishna and his attractive male features, Arjuni became overpowered with love, and she became infatuated with Krishna, entered a state of fascination for him, and even fainted at his sight. Seeing her heightened desire for Krishna, Krishna takes Arjuni’s hand and takes her to the forest. He secretly engages in the Rāsa dance with her and behaves with her like a lover (as he previously did with the Gopis of Vrindāvana). After this experience of pure love, Krishna instructs a reluctant Arjuni to depart and bathe in the enchanted lake again. Arjuni transforms back into the male form of Arjuna. However, Arjuna is dejected and restless as he can no longer enjoy divine love with Krishna. Krishna reassures Arjuna, and by touching him, restores his masculinity.
In the Rāsa dance, Krishna is the only ‘Male’, whereas the rest are female (Gopis). The transformation of Arjuna into a female Gopi is a metaphor for the destruction of the ego (represented by ‘masculinity’) and thus the submission (represented by ‘femininity’) of the soul to the Supreme Lord. It represents the highest stage of Vishishthadvaita Vedanta (qualified non-duality), in which the devotee enjoys the company of the Lord.