The title of the song "Crystal Night" refers to the night of 9th November, 1938 on which the Nazis coordinated an attack on the Jewish people. It is also called "The Night of Broken Glass" because of the shattered glass which littered the streets. In German, this event is called "Kristallnacht".
Why, why do we turn away
When they shout that hymn?
Marching so brave, their hearts beat on boldly right
Their souls belong to those of the weak