Book vs. Movie
To me, this was the most important difference. I thought that "Sophie's choice" was all based around the fact of having to choose between her two kids while in the movie, I felt like the choice was over which man to choose, Nathan or Stingo. The heart breaking decision was a grand total of about two minutes and was never mentioned again in the movie, while in the novel, it was referred to many times because it is what tore her up so bad from her experience in the Auschwitz camp.
Parallels of Racism
Sophie's Choice was primarily about the suffering of the Polish people and how Sophie was a victim of this suffering, but the movie doesn't fully capture this. The movie is more based off of the relationship between Sophie, Nathan, and Stingo more than it is based on the imprisonment of the six million innocent Polish peoples who died as a result of the Nazis.
The absence of the scene explaining that Sophie had been previously raped takes away from all of the hardships that Sophie encountered and her everyday struggles in loving and having sexual relations with men.
This is an important part to leave out of the movie because watchers are unable to grasp how depressed Sophie is from all of the horrid things that happened to her during the Holocaust. As far as the watchers know, Sophie only tried to commit suicide the one time after she was liberated from the concentration camp and was at a refugee camp in Sweden.
Sophie's Lie About Virginity
Although, it is only one simple quote that was absent within the movie, it is important because throughout the movie, Nathan questions her fidelity. Even though Nathan suffers from severe Schizophrenia, he seems to always think that Sophie has cheated on him. Since Stingo is madly in love with Sophie because of the things she says and the way that she acts toward him, it seems appropriate to question her faithfulness to Nathan. By proving how easy she is to lie, it proves the truth to Sophie's morals and character.
Stingo's Father's Visit
The movie did not capture Stingo's character as well as the book did. The visit from his father was important in understanding the character of Stingo and the history behind his motives for his book. In my opinion, the movie mistakes Stingo for being more of a "home-wrecker" type friend instead of sincere.