Keats uses the extended metaphor of exploration to describe that wonderful moment when he first delved into Chapman's translation of Homer. For Keats, reading Chapman's Homer was as much a voyage of discovery as the expeditions of Spanish explorers like Cortez. Much the same could be said of Chapman's original translation process. In the field of translation he too was a pioneer, traversing hitherto strange, unconquered lands. He was the first man to attempt the arduous task of translating Homeric rhythms into English, and Keats's poem, with its extended metaphor of exploration, pays him due homage.
Keats's extended metaphor is also a tribute to the scientific method and its extraordinary discoveries, both terrestrial and astronomical. He makes specific reference to Cortez's sighting of the Pacific Ocean (although it was actually Balboa who made the discovery, but then his name wouldn't have scanned). He also refers to "the watcher of the skies." This relates to William Herschel, the British astronomer who discovered Uranus in 1781.