Context

This serves two purposes: 1) it sets up your point/argument by telling the reader why you’re bringing up a particular source or quote, and 2) it gives the reader information to help identify the speaker or place the speaker or example in the given work.  For example, if using a quote from "A&P," you might say Sammy knew that he was not going to be like a typical hero and "get the girl" at the end of the story. As he walks out into the parking lot, he looks for "my girls," but resignedly notes that "they’re gone, of course" (17). Such a sentence would set up the explanation/argument sentence that follows. The "of course," with its knowing air, suggests that Sammy, even before he stepped outside, realized that his heroic deed would go unnoticed by the girls. Context helps readers by letting readers better understand (and thus agree with) your argument by framing it in a manner so they can understand it.  By setting up your example so clearly, your argument flows logically from your example and explanation leaving the reader with a satisfied "Ahhh" as opposed to a befuddled "huh?"