Why are the Goswamis and their books considered so important in the Krishna consciousness movement?
Krishna Himself appears on earth from time to time, in His own words, to "deliver the pious and annihilate the miscreants." Essentially, He comes to show His attractive, transcendental personality to mankind and thus inspire us to rejoin Him in the spiritual world. To this end, He spoke the Bhagavad-gita, and His pastimes were recorded in the epic Srimad-Bhagavatam. After His return to the spiritual world, mankind largely forgot Him, forgot His teachings, and went back to business as usual.
Then, around five hundred years ago, Chaitanya Mahaprabhu appeared. Scriptures identify Mahaprabhu as Krishna Himself, in the guise of His own devotee. His plan was to revive the consciousness of people in general by again presenting Krishna's instructions for the modern era. Chaitanya Mahaprabhu Himself didn't write books, but He spent considerable time and effort instructing some of His most learned and dedicated disciples in the science of Krishna consciousness. He requested them to preserve His teachings in writing, and expand upon those teachings with their own realizations.
". . . [Chaitanya Mahaprabhu] is Krishna Himself, and He is teaching how to love Krishna. Therefore His process is most authorized (italics added). Just like you [the news anchorman] are the expert in this establishment. If somebody is doing something, if you personally teach him, "Do like this," that is very authorized. So God consciousness, God Himself is teaching. Just like in Bhagavad-gita, Krishna is God. He is speaking about Himself. And at last He says, "Just surrender unto Me. I take charge of you." But people misunderstand. So Lord Chaitanya—Krishna again came as Lord Chaitanya to teach people how to surrender. And because we are following the footsteps of Lord Chaitanya, the method is so sublime that even foreigners who never knew Krishna, they are surrendering. The method is so potent."
Srila Prabhupada also frequently spoke on the essential importance of the writings of the Six Goswamis to those seeking a deeper understanding of the teachings of Krishna consciousness. In his preface to his book Teachings of Lord Chaitanya, a collection of Chaitanya Mahaprabhu's instructions to Rupa and Sanatana Goswami, he has this to say:
"Lord Chaitanya Mahaprabhu instructed His disciples to write books on the Science of Krishna, a task which those who follow Him have continued to carry out down to the present day. The elaborations and expositions on the philosophy taught by Lord Chaitanya are in fact most voluminous, exacting and consistent due to the system of disciplic succession."
And, in the following excerpt from a lecture Srila Prabhupada gave on Chaitanya Mahaprabhu's authorized biography, the Chaitanya Charitamrita, on November 21, 1966, in New York, he had this to say:
"[the six Goswamis] wrote volumes of books on the basis of Chaitanya Mahaprabhu's instructions. Chaitanya Mahaprabhu didn't write any books Himself . . .only eight verses, called Siksastaka. Otherwise, all the valuable books in His sampradaya—philosophical lineage—were written by His disciples, especially Rupa Goswami, Sanatana Goswami, and their nephew Jiva Goswami. Jiva Goswami left home at the age of ten and, after becoming a very great Sanskrit scholar, wrote many valuable volumes of books . . ."
—from a lecture on Chaitanya Charitamrita, Madhya 26.66-96, 11.21.1966
The point is that the Goswamis' literary contributions are given importance because they wrote down Chaitanya Mahaprabhu's instructions on Krishna consciousness. And who better to explain how to develop such consciousness but Krishna Himself, acting as His own ideal devotee?