This line is uttered by Satan in the novel The Master and Margarita at the very climax of the plot. Manuscripts don't burn. Manuscripts remain etched in the mind of those who wrote and read them. The novel is alive in Margarita's mind. It is alive in the Master's mind. Mikhail Bulgakov burnt his own book, this book, The Master and Margarita. It was still written. It still exists. It is a very hopeful line for a novel created by a Soviet author, and a summation of the plot.
Later, this line became commonly used by samizdat producers and other counter-revolutionary or subversive persons. The burning of manuscripts was common. The fragmentation was also common. In a deeply cynical culture, in a deeply cynical time, under pressure from authorities and risking being sent to the gulag, writers continued to write, and remember.
Text is fluid. Stories remain.
Manuscripts don't burn.