Answer:
From which county you belong
engages the reader
teaches the reader something useful (a new way of thinking about the essay in question)
helps the reader to see the bigger picture that the summarized essay is a part of, and
helps you as the writer to gain a deeper understanding of the issues and arguments of the essay being summarized.
To begin with letter 3, It could be said that the main theme is determination because Walton feels confident about the voyage and he is ´determined' to go on with it despite the weather conditions.
As regards letter 4, we might say that the theme may be trust and friendship because Frankenstein and Walton met and he is will to tell him the his story. So this letter might be seen as the beginning of their friendship.
How long does it have to be?
What poem is it cause I am confused