Which humanistic problem did the stiry address?what problem, that is human nature, did the the boook theif have

"The Book Thief" addressed the issues facing the Jews during the Holocaust.  I am not exactly sure what you need.

In the book thief, a young girl, Liesel Meminger, loves to read and learn.  She has been sent to live with a man and his wife after her mother dsappears.  They are poor and rough around the edges.  They provide her with support.  The woman fusses and nags a lot, but she still cares about the girl.  The man is very loving and kind.  The girl quickly bonds with him.

Liesel begins to steal books.  She steals them from the books burned by the Nazi's.  She even steels them from the town mayor.  Liesel's foster mother works for him and his wife washing their laundry.  The woman is very sad having lost a child and is reclusive.

Liesel has a special male friend whom she plays with.  She does not tell him about her Jewish friend.  The air raids begin and are dropping bombs n the town.  She and her foster parents hide with other neighbors in a bomb shelter.  To calm the people she reads or tells them stories that she has read.  Food and work are in short supply.

Liesel's foster father has been asked to return a favor and to hide a Jewish man.  It is in his decision that we find the depth of human nature.  He must decide to take a chance on losing everything in order to protect the man or refuse to follow through.  He chooses to hide the man in his cellar. He can not allow his own child to find out or he would probably become angry.  His son is also disappointed that his father will not register with the political party.  It could mean a better job and some help with rations. The girl befriends the Jewish man and shares her love of books with him..

The Jewish man has to be moved to another place.  Later Liesel sees him being paraded with other Jews through town by the Nazis.  She can stand back or greet him.  She runs to him upset.  She tells her friend the story of the Jew.

The story ends with a bomb that kills Liesel's new family and her friend.  In the end she is taken in by the mayor and his wife.  It is the beginning of the woman's re-emergence into humanity and Liesel's new start in life.

I believe that from a humanistic approach the situation with the Jewish man and having to take a stand to protect one citizen was a momentous decision.  Many people during Nazi times looked the other way and did nothing, but Liesel's foster father is a good man.  He makes a decision that eventually will lead to the survival of the Jewish man following the war.