Srila Vrndavana dasa Thakura describes how Caitanya Mahaprabhu instituted the first Vyasa-puga ceremony in 1509 AD. through Sri Nityānanda Prabhu in Srivāsa Angana, Mayapura, West Bengal:
“Srivasa Pandita, the head priest for the function, gave Lord Nityananda a flower garland to offer to a painting of Vyasadeva. Holding the garland in His beautiful lotus hand, Nityananda Prabhu hesitated and began glancing here and there as if He was looking for someone. Then to everyone’s surprise, Nityananda offered the garland to Sri Caitanyadeva instead. At that moment, Lord Caitanya immediately manifested His six-armed form, sad-bhuja.” (Caitanya Bhagavata (Madhya khanda chp. 5)
Thus, Sri Nityānanda Prabhu completed the Vyasa-puja ceremony by offering a garland to that personality from whom everything emanates and whose empowered incarnation is Sri Vyasadeva. By this Nityananda Prabhu established the real meaning of Vyasa-puja by worshiping the Supreme Lord Sri Krishna in the form of Sri Caitanya Mahaprabhu. Lord Gauranga is the guru of Sri Nityananda Prabhu. Therefore, the worship of Vyasadeva is actually the worship of Bhagavan Sri Krishna and Lord Gauranga in the form of the present acarya.
In the scriptures, Sri Krishna tells Uddhava that the acarya is the manifestation of Himself: “One should know the acarya as Myself and never disrespect him in any way. One should not envy him, thinking him an ordinary man, for he is the representative of all the demigods.” (SB 11.17.27)
If Sri Guru is not regarded as identical with the Supreme Lord, the worship of the acarya is not properly performed, and the said worshiper will not realize the true purport of the following edict from the Shruti: “For one who has unflinching faith in the lotus feet of the Lord, as well as in the spiritual master, the real import of Vedic knowledge can be revealed.” (Shvetashvatara Up. 6.23)
Excerpt from Tribute of Love by Mahanidhi swami