determine two main ideas of the novel and analize their development over the course of the text, including how they interact and build on one another to provide a complex analysis

This is a pretty broad question for this short forum space. It is, however, a thematic question that you can easily look at the themes page which I included below. Pick two themes that you think is important to the book from the list:

http://www.gradesaver.com/the-lion-the-witch-and-the-wardrobe/study-guide/themes