When you're a writer who likes to go off on philosophical rants every now and then, it's great to have a first-person narrator. This way, whenever someone accuses you of being too intellectual or too philosophical, you can throw up your hands and say, "Hey, that ain't me talking. That's the character telling the story." By having Jack Gladney tell the story, DeLillo is able to show us exactly how one man's mind can struggle with fear of death in a world where the truth of things doesn't seem so clear anymore.
At the beginning of the novel, DeLillo gives us a little fake-out. The entire first paragraph is written in third-person, and it feels like that's what we're going to get for the rest of the book: "The station wagons arrived at noon, a long shining line that coursed through the west campus" (1.1). But in the second paragraph, the narrator suddenly drops an "I" on us, and we know we're actually listening to a first-person speaker: "I've witnessed this spectacle every September for twenty-one years" (1.2). This sudden shift helps DeLillo make us question the difference between how things appear and how they actually are, which is a theme he continues to explore for the whole book.