Here is how I would structure this essay: standard 5 paragraphs--introduction, three body paragraphs, and conclusion paragraph.  I am structuring this essay response based on the idea that the major body paragraphs will be about: context, relevance, and views on humanity.

Writing the Thesis:  Rephrase the question.  Some teachers prefer a thesis where you rephrase the prompt/question; some teachers prefer you not do this.  Double-check his/her preference. 

Example thesis:  Harper Lee's novelTo Kill a Mockingbirdcontinues to be timeless novel, reflecting not only its context, but also living on to be relevant and engaging to each new generation, and impacting how the reader's view of humanity.

Body Paragraphs:

1.  Reflection of context--In this body paragraph, pull and analyze quotes/incidents, like Atticus' speech, from the book that depict the moral insight of the novel into discrimination, prejudice, ignorance. 

2.  Relevance-- In this body paragraph, you could choose multiple directions/aspects of the book that make it relevant.  I suggest speaking to it's relevance through the characters.  Students find this book engaging because they relate to the Scout and the Finch family.

3.  Impact on how we view humanity-- One of the predominant themes of the book centers on misconception/misunderstanding. To Kill a Mockingbirdchallenges the reader to ignore previously formed opinions, stereotypes, and prejudice and look at the worth of the individual.  Use Boo Radley and Robinson as primary examples.

Conclusion:  Restate thesis and sub-points.