Revising for theme is a macro-edit but it is odd, in that it will often reveal itself during the micro-editing you do. Theme - what is it? According to the Oxford English Dictionary, the leitmotiv is "a recurrent idea or image in a literary work." The leitmotiv, or thematic symbols, will, if used lightly, register with readers and add a richness to your story, beyond the plot and characters. It will give your work its deeper meaning, like incense offerings enriches the religious ceremony.
Let's say you have several leitmotivs in your work. Let's say I do - I do! I have a medicine bag, hawks and the softness or hardness of landscape in the three locations in the novel. The first two are a bit obvious and I will probably take them down a notch or two as I revise. The last is too subtle and I may try and work it in a bit more throughout the piece. The themes they address are healing, in the case of the medicine bag; wisdom and the freedom it brings, by the hawk presence; and the landscapes reflect the choices Libby has in how she chooses to consider her life.
When we revise, our symbolic patterns become apparent. I think we put them in with some unconsciousness - but we need to polish them and reveal them with finesse. Susan Bell in The Artful Edit, suggests you might highlight them in your text and then see if there are imbalances. She warns "Quantity is not the only issue. Read through your draft to make sure every symbolic image integrates into your text, and does not sit on top as decoration."
Take a piece of writing and have a look at it - see if your leitmotiv shows up subtly or clumsily and what you can do to integrate it smoothly.
And as always - let me know!