This book is tough in all the right ways, meaning you can bet that it doesn't try to be difficult just for the sake of being difficult. (Infinite Jest, anyone?)
In fact, any difficulty you meet will be connected to the difficulties of being a Korean immigrant, an experience that runs throughout the book. Take, for example, language—occasionally, you'll run into a Korean word. Unlike the lived experiences of so many immigrants to America though, An Na holds her readers' hands—as long as you read closely, you'll pretty quickly get through context what those words mean. Na makes a point of it. Which means the toughest part of A Step From Heaven is the emotionally heavy subject matter.
In other words, though the book may have some tough spots, the author helps you through these rough patches. When it comes to your feelings, though, it's between you and your tissues.