Bearing in mind the Mitzvah "Ki Im Besulah me'Amav Yikach Ishah" (Pasuk 14), what is this Pasuk coming to teach us?
Ramban: Pasuk 14 is an Asei to marry a Besulah,
whereas this Pasuk teaches us the prohibition
against marrying a woman who is not a Besulah.
Aassuming that he is not already married.
A La'av that one infers from an Asei is actually an Asei.