Chaitanya Mahaprabhu (or “Lord Chaitanya”) is an incarnation of Krishna who appeared in Nadia, West Bengal, India in the 15th century A.D.
Gaura Purnima is the festival of His appearance that takes place in Spring. The Lord appeared in His previous incarnations as Lord Krishna, Lord Rama, and Lord Narsimhadeva. Lord Chaitanya transformed the hearts of everyone through singing the Hare Krishna Mahamantra and re-establishing the Bhakti Yoga tradition that ISKCON continues through its lineage today. Devotees fast till moonrise on this day, followed by a feast in His honour.
The Supreme Lord Sri Krishna, with the serving mood of Srimati Radharani, appeared as Sri Chaitanya Mahaprabhu to establish Sankirtana Movement – the Yuga Dharma for this age of Kali. He appeared on the full moon day in the month of Phalguna in the year 1486 AD at Sridham Mayapura, West Bengal, India as the son of Sri Jagannath Mishra and Srimati Sachidevi.
When Krishna spoke Bhagavad-gita to his devotee-disciple-friend, the military commander Arjuna, on the battlefield of Kurukshetra around 3,000 B.C., He exhibited all the power and majesty of God Himself. His final instruction to Arjuna was that surrendering to Him is superior to all other religious duties.
Fast forward to late fifteenth century West Bengal, India, the world has had forty five hundred years to ponder (and mostly forget or ignore) Krishna’s appearance and instructions. Krishna’s advice (“surrender to Me”) still stands, but few know how to put it into practice.
In His youth, Chaitanya was known as Nimai Pandit. He gained early fame as the world scholar of the Vedas and was able to defeat all philosophical opposition with logic and argument.
The next phase of His mission was to popularize the public chanting of the Hare Krishna mantra:
Hare Krishna Hare Krishna
Krishna Krishna Hare Hare
Hare Rama Hare Rama
Rama Rama Hare Hare
According to many references in the sacred teachings of the Vedas, chanting this simple mantra is the most highly recommended means of achieving spiritual perfection available in the modern age.
Essentially, Lord Chaitanya is the Supreme Personality of Godhead Himself, appearing as His own devotee, teaching how to best practice Krishna Consciousness by His own most authorized example.
The word Yoga has become synonymous in Western vernacular with a lithe figure, radiant health, peace of mind, and other material benefits. But the original meaning of the Sanskrit term carries a different, higher import: linking with the Supreme.
Srila Prabhupada (Indian Gaudiya Vaishnava Guru & Founder of ISKCON) distinguishes the true goal of yoga—loving devotion to the Supreme Lord—from the physical and psychological elements of yoga practice.
Yoginam api sarvesam
sraddhavan bhajate yo mam
sa me yuktatamo matah
“And of all yogis, he who always abides in Me with great faith, worshiping Me in transcendental loving service, is most intimately united with Me in yoga and is the highest of all.” (Bhagavad-gita 6.47).
Here it is clearly stated that out of all the different kinds of yogis-—the Astanga-yogi, the Hatha-yogi, the Jnana-yogi, the Karma-yogi, and the Bhakti-yogi—the Bhakti-yogi is on the highest platform of yoga. Krisna directly says, “Of all yogis, he who abides in Me with great faith, worshiping Me in transcendental loving service, is most intimately united with Me in yoga and is the highest of all.” Since Krishna is speaking, the words in Me means “in Krishna.”
Vedic texts state that Lord Chaitanya is the Supreme Person, Krishna appearing as His own worshiper. He is the combined form of Krishna and Krishna's most dear devotee, Srimati Radharani. He came to experience the love She feels for Him, and to show by example how to fully surrender to Krishna.
In other words, if one wants to become a perfect yogi on the highest platform, one should keep oneself in Krishna Consciousness.
The message of Lord Caitanya Mahaprabhu was to give the same message as Krishna in the Bhagavad-gita: "surrender to Krishna".