To accurately determine the central idea communicated by the playwright in the excerpt, it would be necessary to analyze the specific content and context of that excerpt. However, based on the options provided, if the focus is on the nature of the characters and their development, it is plausible to suggest that the statements about Grendel or the warrior might indicate their respective strength or determination.
If you can provide more context or details from the excerpt, I could help you better identify the central idea. Otherwise, based on just the options, "The playwright communicates that the warrior will be persistent" might reflect a common theme in narratives involving battles or conflicts.