Who was the devotee who was always thinking of Krsna the most? Always speaking about Him? She was none one other than Srimati Radharani. She is always absorbed in thoughts of Krsna. So Lord Caitanya appeared and He adopted the mood of Radharani, the topmost devotee who is always thinking of Krsna and is always serving Krsna.
Why Lord Caitanya Tries to Remain Hidden - Gaura Purnima, February 28, 2010, Budapest