"Go to Judea" basically means "leave the backwater of Galilee and go to where the real action is happening" - Jerusalem, the center of power and religious authority.
Jesus' brothers didn't believe in him, so this seems to be a ploy to get him to "put up or shut up." If you're really the Messiah (which essentially means anointed king), then you actually need to go take up your throne in Jerusalem. If you don't, then please stop embarrassing yourself…and us.
This paragraph also indicates John's awareness of the literary concept of the "messianic secret," which is Jesus' usual modus operandi, particularly in the Gospel of Mark. Think of all the times Jesus heals someone and then tells them not to tell anyone. Basically, Jesus is being the master strategist, making sure that if "his time has not yet come," he doesn't tip over the dominoes too quickly on his way to Golgotha.
Fascinatingly, Jesus lies! He says he's not going to the festival and then he does. Not to split hairs too much, but lying in the Hebrew Bible is usually constructed around bearing false witness against a person or breaking a covenant/oath. Basically, deception with intent to harm. This lie of Jesus seems to be more of a stratagem to keep himself out of harm's way. Again, not to knock over the dominoes too quickly.
John also tells the story of Jesus' popularity in reverse compared to the other Gospels. Whereas Jesus enters Jerusalem fully one time in triumph in the other Gospels, in John he enters Jerusalem three times, and his popularity shrinks over the trajectory of the story. By the time of the last week of Jesus' life and the final entry into Jerusalem, John goes to pains to tell us that the only reason there's a crowd at all is because of Jesus raising Lazarus. Basically, the crowd is there because they want to see a sign, not because of Jesus himself or messianic expectations applied on to him.
Aside: if Jesus can still talk to his brothers (despite a pretty significant difference of opinion about who Jesus is), I suppose I can still talk to my family, despite our comparatively smaller differences of opinion! hahaha