LitCharts assigns a color and icon to each theme in The Book Thief, which you can use to track the themes throughout the work.
Death
Words and Language
Books
Stealing and Giving
Color, Beauty, and Ugliness
Summary
Analysis
Death describes a future scene with Rudy, where he is diving into the cold Amper River to fetch a book, and then standing in the water, asking Liesel for a kiss. Death then reveals Rudy's death, which will take place two years later among piles of rubble.
This seems to give away the ending, but it also is a reminder that death awaits everyone – even so, the reader's knowledge of Rudy's death make his part in the rest of the novel seem more tragic.