What is the author's purpose for characterizing the Nazis terrorizing Josef's family as "shadows"? (1)

The novel opens with a frightening scene in which Josef's family's apartment is broken into in 1938. Josef's father is accused of illegally continuing his law practice despite recently enacted laws that prohibit Jews from practicing law. Rather than describing the Nazis' faces, the author describes them instead as shadows, saying, "Towering shadows burst into the room" (1). Josef is then attacked, as detailed when the narrator states, "He kicked and flailed in a panic, but one of the shadows caught his ankle and dragged him face-first across his bed" (2). The author's decision to use the word "shadow" (1) to describe the Nazis underscores their dark motivations and also the family's terror and uncertainty during this attack on their home and persons.