There are several things you will need to consider as you write your essay about To Kill a Mockingbird by Harper Lee. The first is which particular timeless issues you wish to discuss. An important consideration is what makes an issue timeless. The specifics of racial conflict in United States are obviously not timeless, as they are symptomatic of a specific place (the southern United States) and time period (the past few hundred years). Instead, you might think about whether discrimination is a universal issue. Do all human societies have privileged groups and oppressed minorities? In what ways do general prejudices about minorities influence the way we treat individuals belonging to those groups? As you think about these questions, you will want to consider not just the racial issues in the novel and the case of Boo Radley, and the poor rural families such as the Ewells.
Evaluative language means that you should introduce your own judgments into the essay rather than writing in an impersonal voice. This might mean, for example, stating that "the novel is not only effective in portraying the effects of racism, but also give the reader a clear and critical view of other forms of class and gender oppression common in small southern towns of the period."