Is The Significance And Theme Of A Novel The Same?

No, they're not. The theme is literally what it's about, the subject-matter whereas the significance is the message. Of course they'e linked but they're not exactly the same. I teach creative writing now and was a Literature teacher for 12 years previously and I found a lot of people get these two mixed up. I might offer you a specific example to illustrate - take the novel, `Jonathan Livingston Seagull.' The story (plot) is about a seagull who's different and ends up isolated from his community; the theme is loneliness and alienation; the significance is that Jonathan, representing all of us in society, is gaining self-knowledge through his pain. Both of these components in a novel are essential to the execution of the work. Understanding the theme is one of the most important aspects of studying literature because it contains the depth of the author's message. The significance is probably more of an overall idea of its meaning.
I hope I have explained it clearly for you.