One of the most powerful opportunities of the novel format is the ability to describe what a character is thinking. In movies or stage plays (with exceptions) you must show what the character is thinking through action and/or dialog. But in a novel, you can just come out and say it.
For example, in a movie, you might say:
John walks slowly to the window and looks out at the park bench where he last saw Sally. His eyes fill with tears. He bows his head and slowly closes the blinds.
But in a novel you might write:
John walked slowly to the window, letting his gaze drift toward the park bench where he last saw Sally. Why did I let her go, he thought. I wanted so much to ask her to stay. Saddened, he reflected on happier times with her – days of more contentment than he ever imagined he could feel.
The previous paragraph uses two forms of expressing a character’s thoughts. One, is the direct quote of the thought, as if it were dialog spoken internally to oneself. The other is a summary and paraphrase of what was going on in the character’s head.
Most novels are greatly enhanced by stepping away from a purely objective narrative perspective, and drawing the reader into the minds of the character’s themselves.