"Let's discover the Galilee
with Mozart "
Mozart: The gifted composer
Although Milos Forman's movie is not Mozart's "biopic," the clip from the movie you can find on YouTube: https://www.youtube.com/watch?v=th_ro9CiASc describes Mozart's extraordinary gift well enough.
On his scores, no erasures, no "repentance" ...
Franz Xaver Niemetschek describes the composer as follows:
“Mozart wrote everything with rapidity and lightness which might, at first glance, seem like ease or haste. ... His imagination presented the entire work to him, sharp and vivid as soon as it was started. His great knowledge of composition allowed him to embrace all harmony in one look. You rarely find crossed out passages in his drafts ... The work was always finished in his head before he began to write it. When he was given words to set to music, he would take care of them for a long time, think deeply, then let his imagination run wild ... For him, writing was thus an easy job, during which he often joked and had fun. "
Johann Friedrich Rochlitz also describes the art of Mozart as follows:
“This does not mean that Mozart worked quickly or lightly, as he was playing around. When he had something big or important to write, it rarely came to him on time and as if it had fallen from the sky ...
During his frequent car trips, Mozart used to not only let his imagination run wild on new melodic ideas, themes ... but also to occupy his mind and his sensitivity to immediately put in order and work out what he had found, so that unconsciously, he often hummed or even sang at loud ...
So he was finishing whole pieces in his head, carrying them within him until the moment he had the opportunity to write them or the will to get rid of them all at once. "
In their comments Jean and Brigitte Massin believe that if the supposed remarks made by Mozart were perhaps a little arranged by Rochlitz, the general direction of the speech seems to have a good chance of being authentic.
We think there is nothing more to add ...
 From the notes and extracts taken from the Mozart bibliography by Jean and Brigitte Massin.
 Professor of philosophy at the University of Prague, he took charge of the education of Mozart’s second son and, using documents provided by Constance Mozart, wrote the first monograph devoted to Mozart and dedicated by Haydn.
 Johann Friedrich Rochlitz is a German playwright, friend of Goethe, Schiller, also a musicologist and art critic. Known for having spread many anecdotes which contributed to the formation of the popular image of Mozart but whose authenticity is analyzed with reservations by biographers, his words reported here corroborate those of F.X Niemetschek.