Secret of Rasa Lila
Rasa Lila is divine sport  with the devotees for bringing about their union with the Lord through Prema or pure divine love. Rasa is the sweetest juice of Prema. It is the manifestation of divine love or higher emotion which takes the devotee to the magnanimous height of holy communion with the Lord.
Lord Krishna’s Rasa Lila is the mystery of mysteries. It is the secret of secrets. It is not a matter for intellectual discussion. It is a holy matter for silent meditation for devotees. It should not be divulged to insincere critics or those who have no devotion to the Lord. It should be studied with reverence and faith. It contains Madhurya Rasa, the crowning glory of Bhakti, which leads to absolute self-surrender and absorption in the Lord.
Sri Krishna performed the Rasa Lila to destroy carnality by means of pure love or Prema. He taught humanity through the Rasa Lila how to convert passion into dispassion and pure love, and how to wean the mind from the sexual Vasanas and instincts. He showed that through Madhurya Rasa one can effect total self-surrender or Atma-Nivedan, and attain Sayujya or absorption in the Lord or husband of our hearts.
Rasa Lila was a sport  which was meant to build up the faith, to strengthen spirituality towards holiness, to improve the minds of the Gopis in particular and humanity in general.