Successful stories are often ones whose elements are employed subtly. You may not be able to say exactly why they work, and as a reader, you probably don’t care; you just like the feeling of rightness that settles in as you read. Theme is one of those important elements that are quietly working in the background of a strong story. It is pulled deliberately or subconsciously from the author’s individual worldview, and acts as an anchoring thread that connects the other elements and creates a sense of cohesion. 

The theme of a story is the central message that explores a universal concept: isolation, family, redemption, addiction. These ideas are common to the human experience, and when we include them in our writing, readers find themselves engaging with those ideas and connecting with the text and the characters on a deeper level. But thematic ideas themselves aren't typically so ambiguous. The author often brings their own worldview and perspective to bear on these concepts to form a thematic statement that supports a specific opinion.

Love conquers all. (Sleeping Beauty)