This is really unexpected. The Development section has just been powerfully closed, and we were waiting for the Recapitulation to begin. Instead, Beethoven dramatically quotes the whispered repeat note and Fate Motive of the Third movement. It seems like a sudden recollection of anxious feelings from the past.
Beethoven not only brings us back to the end of the Third movement, but even changes the meter to the three beat Scherzo meter. Here, after the exciting experiences of the Fourth triumphal movement, the Scherzo theme does not sound ghostly and threatening anymore. It sounds more like a dim memory of a battle which has been won.
