The special function of Srila Rupa Gosvami is to establish the feelings of Sri Caitanya Mahaprabhu. These feelings are His desires that His special mercy be spread throughout the world in this Kali-yuga.

prthivite ache yata nagaradi-grama
sarvatra pracara haibe mora nama

His desire is that all over the world everyone, in every village and every town, know of Sri Caitanya Mahaprabhu and His sankirtana movement. These are the inner feelings of Sri Caitanya Mahaprabhu. Sri Rupa Gosvami committed to writing all these feelings of the Lord. Now again, by the mercy of Sri Caitanya Mahaprabhu, the same feelings are being spread all over the world by the servants of the Gosvamis…. Those who are on the level of hogs and dogs will never appreciate such a great attempt. Yet this does not matter to the preachers of Sri Caitanya Mahaprabhu’s cult, for all over the world they will continue to perform this responsible work, even though persons who are like cats and dogs do not appreciate them.

From Srila Prabhupada’s purport to Cc. Antya 1.117