Truthfully whether you "get" it or not theme is one of the most important things about a story and is integral to plot. Theme is the reason you write the story. It is what you, as the author, are telling the world. Knowing and understanding the theme you are exploring in your work will keep you on track and it will help you explain the work to agents and editors.
According to Suite101.com, there are two kinds of themes in writing, implied truth themes and simple themes. Most of my books have implied truth themes such as "love will prevail but it's not always easy," or "you are more than you think you are," and "no where is safe." Simple themes are one word themes such as "courage," "survival," "friendship," "sacrifice," and "growth."
Once you have identified your working theme be sure to state it early on in the work. Perhaps not literally but strongly.
Ex: one character can say to another, "there is more going on here than meets the eye." And the other can answer with a shake of the head, "you are one of those conspiracy theory crazies, aren't you?"
Or a character can pass a man on the street holding a sign that says, "The end of the world is near." Even if it's only the end of the character's marriage or career. It states the theme of the book. And begs the question, now what?
Putting theme into words is one of the hardest parts of story telling and yet, if you take the time to discover your theme, it will give you a clear path to follow whether you plot or pants your story. It will also help you with your tag line, synopsis and pitch. Don't just ramble, people, know what it is you want to say and then make sure you say it in a clear and concise manner.
Does theme come easy or hard for you? Do you find what you think is your theme but then readers find something else in your work? Does your theme change over the course of your writing? Curious minds want to know. Cheers~