3 Examples of Figurative Language:
Irony: When they found out Dumbledore left them clues and a tool to destroy the Horcruxes they were extatic, but then Ron left the group to go home. It is ironic in that something so bad happened when something so good happened.
Symbol: The rain and the gloomy downpour started to come right when an angry and nasty conversation was approaching. The rain is a symbol of bad things happening.
Onomatopoeia: When a spell was cast by the death eater Yaxley, the sound described was BANG.
I believe that one emerging theme in the book is determination. Determination is a thing that is being challenged right now for the group, and if they prevail and stay determined rather than give up, it will be a moral of the story if all works out.