Themes and Motifs
Themes are wider subjects of your story. If plot is what happens in the story, the theme is more like what the book is about – a deeper subject that your plot helps to highlight.
Themes can include revenge, oppression, power, ambition, coming-of-age, death, pride, prejudice, etc.
Motifs are repeated elements that emphasise your theme and are symbolic of your wider themes.
If darkness is consuming your character – you could use the weather to highlight this. Have the weather darkening or growing cold around them.
If your character is dealing with death, a popular motif for a lost loved one is feathers.
A motif signposts the theme to the reader, subtly and with control. A motif adds emphasis to the idea you are trying to work into your story.