Throughout the Inferno ,Dante's states of mind changes drastically from when he first enters hell up to canto V.
As he experience More and More torture and suffering throughout hell,his perspective and attitude is transformed.
“an unobstructed passage to the Atlantic”
This "unobstructed passage to the Atlantic" allows for access "to every quarter of the world." The ability to reach every part of the word allows for Britain to trade with anyone and everyone. It best supports the thesis that Britain's geographic advantages supported trade. The detail "insular [inward looking] situation" makes Britain seem closed off as it is focused on it being inside itself rather than open to others. "Combined with the command of the seas" indicates that Britain has access to the seas, but doesn't show how far reaching it goes. "Secures our territory from invasion" would be better to prove that Britain is well protected and safe from invading forces.
