It is told that Rabbi Shimshon of Ostropol, who is famous for his two books on Kabbalah, decided one day to write a com¬plete kabbalistic commentary on the Talmud, to explain the secret and hidden meanings of this enormous body of Jewish learning.
He made good use of his knowledge of esoteric wisdom and completed the complex work after considerable labor.
But being a very holy man, he subjected the book to the test of a dream, she'eilat halom, and the answer he got to his questions was that his work was too lengthy and elaborate.
He made it shorter and again posed the question.
The answer was the same: too long.
Again he cut his work down, and again he was told that it was not sufficiently precise and clear.
When he had made it as short and concise as he could, he discovered that what he had written was Perush Rashi, the accepted commentary on the Talmud.
–Rabbi Adin Steinsaltz
From On Being Free, p. 183 by Rabbi Adin Steinsaltz