On First Looking Into Chapman's Homer
At the start of the poem, Keats tells us that he's no backwater bumpkin; he's read lots of books and seen all the different worlds that authors can create. Particularly, he's heard and read a lot about the world of the ancient Greeks and all the surrounding areas. He's even heard of Homer (no, not that Homer, this Homer. That's just a set-up, though, as he explains that he never truly experienced that world until he read Chapman's translation of Homer's work.
When he read that book, it was a moment of pure discovery. He tells us that he felt like an astronomer who just discovered a new planet in his telescope, or like the explorer who stood on the western edge of the Americas and looked out on the Pacific Ocean for the first time. Way to knock it out of the park, Chapman.