Nakula Bramachari became empowered by the Supreme Lord and the Supreme Lord manifested Himself in Nakula Bramachari and suddenly Nakula Bramachari began to show the same qualities of Caitanya Mahaprabhu. He became effulgent. He developed extraordinary symptoms of love of God. Sometimes he was acting like a madman, confused, tears were rolling from his eyes and sometimes he was just so ecstatic that everyone was amazed!
So sometimes, Lord Caitainya, in order to preach Krsna Consciousness, is manifesting Himself in another person and this is called the Aveshya of the Lord when He is manifesting His energy into another being.
(Kadamba Kanana Swami 2003)