Read the full text of Cymbeline Act 3 Scene 3 with a side-by-side translation HERE.
In the woods in Wales, Belarius tells Guiderius and Arviragus to worship the sun and the heavens.
Wait, who are these dudes? Don't worry—you haven't missed anything. We're just meeting these guys now.
Belarius tells the young lads to go up to the hill to hunt while he goes on the flat lands.
Guiderius knows Belarius is older and wiser, but sometimes he wants to go somewhere other than the woods. He's bummed that he's ignorant about everywhere else.
Arviragus agrees. He wonders what they will even talk about when they are as old as Belarius. They won't have any experiences to share.
Belarius tells Guiderius and Arviragus the city is full of bad people. Then he recounts a time when he lived in the city and Cymbeline loved him. But then people proclaimed him to be a friend of the Romans, and he was banished.
That sucks, Guiderius says, and then he and Arviragus run off to hunt.
Once they are gone, Belarius lets us in on a little secret: Guiderius and Arviragus are actually Cymbeline's sons. No way. Not only does Cymbeline think they're dead, but the boys think they are actually the sons of Belarius.
Belarius tells us that after Cymbeline unjustly banished him, he decided to get back at the king by kidnapping his boys. He goes by the name Morgan now, and he's raised Guiderius and Arviragus ever since he kidnapped them.
And by the way, Belarius has renamed the heir (that would be Guiderius) Polydore and his younger brother (Arviragus) Cadwal. Just to repeat: the boys' real names are Guiderius and Arviragus, but Belarius—who goes by the name "Morgan"—calls them Polydore and Cadwal.