What is the effect on the reader of moving back and forth between the stories from different periods of history?

The novel is broken into three different third person perspectives in order of Josef, Isabel, and Mahmoud. He writes this order because it follows sequentially in time - Josef starting in 1938, Isabel in 2994 and Mahmoud in 2015. Each perspective is broken into several pages - some no longer than four pages, some longer than 7. The length of the perspective does not necessarily indicate the gravity or importance of that part of the child’s story. Gratz repeats this order - Josef, Isabel, Mahmoud, Josef, Isabel, Mahmoud - until the very end of the novel when he stops telling Josef’s perspective. He does this for two reasons. First of all, Josef dies, therefore his perspective ends. And second, Mahmoud and Josef’s story collide in the end so he is telling one story now through them both.