 Why did the Viceroy blockade the Earth if he wanted an Earthling to come and meet with him?
The sight of an Earthman on Vega III, where it was impossible for an outlander to be, brought angry crowds to surround John Crownwall as he strode toward the palace of Viceroy Tronn Ffallk, ruler of Sector XII of the Universal Holy Empire of Sunda. He ignored the snarling, the spitting, the waving of boneless prehensile fingers, as he ignored the heavy gravity and heavier air of the unfamiliar planet. John Crownwall, florid, red-headed and bulky, considered himself to be a bold man. But here, surrounded by this writhing, slithering mass of eight-foot creatures, he felt distinctly unhappy. These humanoids had large mouths and sharp teeth, and they unquestionably slavered. If they carried out the threats of their present attitude, Earth would have to send Marshall to replace him. The clashing teeth of the noisiest of them were only inches from the quivering flesh of his back as he reached the upper level. Instantly, and unexpectedly to Crownwall, the threatening crowd dropped back fearfully, so that he walked the last fifty meters alone. A pair of guards, their purple hides smoothly polished and gleaming with oil, crossed their ceremonial pikes in front of him as he approached the entrance. "And just what business do you have here, stranger?" asked the senior of the guards, his speaking orifice framing with difficulty the sibilances of Universal Galactic. "If you mean His Effulgence, Right Hand of the Glorious Emperor, Hereditary Ruler of the Seventy Suns, Viceroy of the Twelfth Sector of the Universal Holy Empire"—Universal Galactic had a full measure of ceremonial words—"he sees only those whom he summons. "Just tell him that a man has arrived from Earth to talk to him. Crownwall sat on the steps, puffed alight a cigarette, and blew expert smoke rings toward the guards. An elegant courtier, with elaborately jeweled harness, bustled from inside the palace, obviously trying to present an air of strolling nonchalance. His Effulgence commands you to appear before him at once." The two guards withdrew their pikes and froze into immobility at the sides of the entrance.
 The blockade was a test to see if Earthlings were smart enough to help the Vegans defeat the Sundans.
 The blockade was a test to see if Earthlings were smart enough to help the Vegans defeat the Sundans.  The blockade is there to protect Earth from the Sundans.  The blockade is there to quarantine the Earth. Earthlings may have diseases that could infect the other races.  The blockade is there to keep people from leaving the Earth.