Lord Sri Caitanya Mahaprabhu is Krishna appearing in the mood of Srimati Radharani. Krishna could not understand the feelings Radharani has for Him and the distress she felt when she was separated from Him. So to experience the mood of Srimati Radharani Krishna Himself appeared with a golden complexion in the mood of Srimati Radharani. Lord Caitanya popularized the chanting of the Hare Krishna maha mantra and declared that this chanting of the Hare Krishna mantra is the only way to make spiritual advancement in this dark age of Kali-yuga.