How do Bruno and Shmuel demonstrate the essence of friendship despite their many differences? What are their differences

The only difference is that Shmuel was born a Jew and Bruno was born German. Their situation is born out of the tragedy of Nazi Germany and WW2. The author has used innocence to describe atrocities that are indescribable, to create a story of two boys who in their similarities and their friendship question the cruelty of humanity in a way that causes the reader to see the world through fresh eyes. Innocence is extremely important in the plot of this novel not only because of the subject matter, but also because if Bruno had better understood what his father's job was and what Out-With truly was, he would not have found himself in the situation that led to the climactic finale of the book.