Anovel’s narrative voice can be most easily recognized through

imagery
style
theme
tone

It would be TONE not theme because to get the "narrators voice" since you cant hear the him/her speak you have to go by the TONE of the story.

- "chilles is sad and angry because hector, the trojan leader, killed his best friend patroclus. he seems angry with himself because he didn't or protect patroclus against the trojans."