Keys. They unlock stuff. Like gates. Which keep people out. In Ready Player One these gates are nested inside one another. You can't open one without opening the one before it. Not only does it lead Wade and friends closer to their goal—Halliday's Easter egg—but it also leads Wade further into his obsessions.
With each gate, Wade gets a little crazier about finding the egg. He locks himself away in an apartment without sunlight. He shaves off all of his body hair. He sells himself into servitude to IOI as part of his master plan. By the end of his journey into a digital wonderland, Wade emerges looking less like the white rabbit and more like a naked mole rat.
Because of this, these gates are almost a dual symbol. They show progress in Wade's journey toward the Easter egg and truckloads of cash, but they also show a kind of regression as Wade becomes more and more of a creepy, anti-social hermit. We guess gates can lead into something just as well as they can lead out of it.