The most of the letter is written using the structure of a compund sentence, because a coordinating conjunction is used in most of the main sentences,which in this case, is the conjunction "and".
The use of "and" to join the sentences that elaborate the arguments on the letter,eliminate th possibility of creating a complex sentence structure,because fort his,it isnecessary to have a sentence which depends of another one, both coupled by a suordinating conjunction, for instance before, even though,although after, because etc, which are not used in the passage.
The overriding idea in any piece of fiction is known as its theme. It tells us what the piece of literature is about, what happens, what ideas the writer wanted to convey, etc.
