I'm thinking more "Secrecy", but this is close too.

...and choices too. Maybe Isolation too. A little of most of them actually.

The majority plays some part in it, but I think the overriding theme is the love between Edward and Bella.

Love is so big in that book.

I think because Twilight was introducing the concept of vampires and what Edward really could do to Bella, Strength and Skill are a big part. It also shows how hard Edward has to concentrate on staying focused around her and not "crossing the line", especially when it came to their first kiss. Twilight really does focus on the vampires' strenth and skill in the fighting scene and also the whole scene where Edward and Bella are up in that tree. (well, obviously some of my response had to do with the movie).