Why is Peter Corrie's favorite nephew in The Hiding Place?

As "a dutiful aunt", Corrie tries to love all her nieces and nephews equally, but from the time he is a child, Peter stands out in her mind.  Bold and spirited, and a musical progidy as well, Peter, from the age of thirteen, is "the pride of (Corrie's) life" (Chapter 1). 

Peter shares with Corrie a love of music, particularly in playing the piano.  As an eight-year old, Peter first displays his uncanny talent in music, noting matter-of-factly that one of the notes on the piano that is playing a Brahms concerto on the radio is flat.  When the family realizes that he is right, Corrie spends the rest of the afternoon "sitting beside Peter on the piano bench giving him simple musical quizzes, uncovering a phenomenal musical memory and perfect pitch".  Corrie teaches Peter what she knows about the piano for six months, by which time "he had learned everything (she knows) and (goes) on to more expert teachers" (Chapter 4).

Peter's audacity and boldness endear him to Corrie's heart, but his devil-may-care approach to life frustrates her, even as she is charmed by his practicality and straighforwardness.  Peter is the organist at the Ten Booms' church, but, to his Aunt's consternation, most often pays little attention to the sermons during the services, regarding them as interesting "only to venerable relics like his mother and (Aunt)".  One day, he makes a bravely defiant but dangerous gesture in church, playing "without preamble...(at) full volume", the Dutch national anthem, against specific German prohibition.  Although many consider him to be a hero for his action, Corrie thinks of it as a risky "moment's meaningless defiance".  In truth, Peter is arrested and imprisoned a few days later, and spends "two months in a concrete cell".  When he finally is released, he comes home with the irrascible spirit which so endears him to his Aunt Corrie unbowed; he is "thinner, paler, and not a whit daunted" by his incarceration (Chapter 6).