Chapter 1: Section 3: Page 24: Line 51 (336)

 Presently they had come within view of the searchlight beams sweeping the skies from the roof of the immense Manufactures and Liberal Arts Building—a miniature city, nested within the city-within-a-city which was the Fair itself—and began to see caped Columbian Guards on patrol, a reassuring sight, to Lindsay at least.

* * * * * * * * * *

"the searchlight beams sweeping the skies"
This statement, along with the later reminder that this is a city within a city within a city—cities all the way down—is a reminder of Matthew 5:14 (which is also a reminder that all references ultimately go all the way back to The Bible—it's Bible quotes all the way down!) and the "shining light" of "the city on a hill." I could also say it's a reference to Ronald Reagan or John Winthrop but since they were ultimately referencing The Bible, it's only speculation that Pynchon is referencing them but safe to assume he's referencing The Bible.
    The exhibits on display in the Manufactures and Liberal Arts Building are meant to provide knowledge of technologies and ideas that will lead the people of the world into a better future. It is an example to be broadcast to the masses and, being that it's a Biblical reference, apparently to save them. It is the way forward while the exhibits surrounding the building, especially those in the darkest and least lighted alleys, are the past. This is the future center of the world and it's as white and as male as every white male always knew it would be (because exhibits by women were forced into their own building and African Americans weren't really represented at any level of planning for the Fair and its exhibitions).

"the immense Manufactures and Liberal Arts Building"

Imagine building this as a temporary structure.

Yes, I know that a lot of temporary structures from World's Fairs wound up becoming permanent structures (like the Eifel Tower and the Space Needle (not to mention many temporary buildings to house people and tourists which became permanent apartment buildings)). And this building might have become permanent as well if it hadn't burned. But the idea was that every building at a World's Fair was theoretically temporary. And yet they were still built this magnificently and grand. Impressive.

The interior which shows how it's a city within a city within a city.

"see caped Columbian Guards on patrol, a reassuring sight, to Lindsay at least"
And if the reader still doesn't understand just how xenophobically myopic the entire enterprise ultimately is, we see Lindsay finding comfort in guards representing Columbus patrolling the streets of the Fair. Police have always been a reassuring sight to those people who know exactly who the police are policing.
    This celebration of the advancement of white males (specifically the non-poor ones) can also be read in the insular nature of the description in this sentence: the cities inset within other cities. This is the way toward exclusion. The only way to whittle down a city to fit within another city is by exclusion which is on full display here at the Fair. First off, people must pay fifty cents to enter. So you've now excluded the poor, almost certainly immigrants. You then exclude further by keeping the non-white exhibits to the periphery of the inner city, making another city toward center, the White City to be specific. And even in this interior city, you can exclude further, right down to a single building which exclusively housed white male exhibits. Imagining this movement further, "beyond the zero," one might say, you can see the trajectory continue until the final, smallest city becomes "a white male, preferably American."
    While the Chicago World's Fair might have been celebrated as a coming together of cultures and people from across the globe, ultimately it simply becomes a statement of white male authority.