What is the difference between central idea main idea, and theme? please makes the answer not too wordy

A central idea is a main point that the author is making.

The main idea is the point of the paragraph or topic.

The theme in a story is its underlying message, or 'big idea’. This would be like a story of a group of guys hating on the new kid because he wears old clothing and they assume he’s poor but turns out the kid is rich and just likes to dress up like that. The theme here would be “don’t judge a book by its cover”

1. read the following excerpt from franklin d. roosevelt's "fireside chat 19":

on the other side of the picture, we must learn also to know that guerilla warfare against the germans in, let us say serbia or norway, us; that a successful russian offensive against the germans us; and that british successes on land or sea in any part of the world strengthen our hands.

remember always that germany and italy, regardless of any formal declaration of war, consider themselves at war with the united states at this moment just as much as they consider themselves at war with britain or russia. and germany puts all the other republics of the americas into the same category of enemies. the people of our sister republics of this hemisphere can be honored by that fact.  

the true goal we seek is far above and beyond the ugly field of battle. when we resort to force, as now we must, we are determined that this force shall be directed toward ultimate good as well as against immediate evil. we americans are not destroyers — we are builders.

analyze the effectiveness of this excerpt. how does it function within the speech as a whole? how does the structure of the excerpt to convey the speech's purpose and key points? support your argument with evidence from the speech. (10 points)

a. the scene is structured as a dialogue between two characters in their own informal language.