Which statement best captures the main argument of the letter?

What is the main theme of the letter
The main theme of the letter - this is the main issue that has set itself the author, or the basic statement that he proves throughout the whole text.
The main theme of the text develops mikrotemah that can knock down with a definition of the main theme. Therefore, if the author does not explicitly specify the main theme in the title of a work, to determine the main theme can often only read the text in full.
What is the main idea of the text
The main idea of the letter - is concisely formulated the subject content and analyzing its main feature.