The main idea of this excerpt is the fact that the Grimm Brothers had a strong belief (that the most natural and pure forms of culture were linguistic and based in history) and in following it, they <em>saved</em> the fairy tale. In order to do so, the author gives a supporting detail and reveals the main idea, followed by more details.
After Caesar was stabbed to death, the conspirators along with Brutus explained why Caesar had to be killed.
You have the right to practice your religion freely
"To war and arms I fly",
"The first foe in the field"
''that from the nunnery''