A book's theme is usually derived from the emotional development of characters or from the consequences these characters face as a result of their actions. By using your theme in the right way, you end up creating an emotional connection between your readers and characters.
The question pops up in everyone's mind at least once in their life, Is all this technology controlling us or improving our lives? Many people believe it's controlling us. Personally, I believe that it improves our lives because...(enter your reasons)