Lord Caitanya appeared for three principal purposes of His own.
1.The first purpose was to relish the position of Srimati Radharani, who is the prime reciprocator of transcendental love of Sri Krsna. Lord Krsna is the reservoir of transcendental loving transactions with Srimati Radharani. The subject of those loving transactions is the Lord Himself, and Radharani is the object. Thus the subject, the Lord, wanted to relish the loving mellow in the position of the object, Radharani.
2. The second reason for His appearance was to understand the transcendental mellow of Himself. Lord Krsna is all sweetness.Radharani’s attraction for Krsna is sublime, and to experience that attraction and understand the transcendental sweetness of Himself, He accepted the mentality of Radharani.3.
3. The third reason that Lord Caitanya appeared was to enjoy the bliss tasted by Radharani. The Lord thought that undoubtedly Radharani enjoyed His company and He enjoyed the company of Radharani, but the exchange of transcendental mellow between the spiritual couple was more pleasing to Srimati Radharani than to Sri Krsna. Radharani felt more transcendental pleasure in the company of Krsna than He could understand without taking Her position, but for Sri Krsna to enjoy in the position of Srimati Radharani was impossible because that position was completely foreign to Him. Krsna is the transcendental male, and Radharani is the transcendental female. Therefore, to know the transcendental pleasure of loving Krsna, Lord Krsna Himself appeared as Lord Caitanya, accepting the emotions and bodily luster of Srimati Radharani.
Lord Caitanya appeared to fulfill these confidential desires and also to preach the special significance of chanting Hare Krsna, Hare Krsna, Krsna Krsna, Hare Hare / Hare Rama, Hare Rama, Rama Rama, Hare Hare, and to answer the call of Advaita Prabhu. These were secondary reasons.