This rule ought to be pretty easy to keep straight: When you write about literature, you always use the present tense when you write about the events from within the literature. If it helps, think of it this way: When you pick up Romeo & Juliet, even if the play takes place hundreds of years ago, your reading of it is taking place RIGHT NOW, so Romeo is falling in love with Juliet, and the families dispute with one another.
There are only two examples of when it becomes acceptable to use the past tense in a literary essay:
1) When you are writing about a specific historical event. It just sounds ridiculous to speak about historical events in the present tense, like the following: “The reference to dazzle paint, which the British navy uses in World War Two, is significant at the end of The Lord of the Flies”
2) When referring to two different moments in time within a single sentence. It is correct to say “Esperanza remembers when her aunt moved to Chicago” – to change this second verb to the present tense would change the meaning of the sentence entirely. If the two moments in time get split into two different sentences though, both events should be written about in the present tense. So it is better to say, “Esperanza remembers many details about her aunt’s arrival. Her aunt, on the other hand, forgets her passport when she moves to Chicago.”
The only verb-tense mistake worse than writing a literary essay in the past tense is to bounce randomly back and forth between past and present tense.
Finally, you should never change the tense of a quote from a novel / play / poem simply because it was written in the past tense. If Romeo speaks in the past tense, and you quote him, don’t change his words because of this essay-writing rule.