Fifty gates of Bina:
There are fifty levels of Bina, understanding. These fifty gates exist both in Kedusha and in Kelipa. When the Jewish people were in Egypt, they entered into the depths of evil, close to the 50th gate, and Hashem had to remove us from all these gates of evil to bring us to accept the Torah. It is for this reason that the Torah states the concept of Yetzias Mitzrayim 50 times, in order to remove us from the fifty gates of evil.
 Siddur Im Dach p. 16