A strong love story. For example, in a novel, if the couple overcomes great difficulties like in 'Romeo and Juliet' (although it's a tragic ending in a sense but the love is strong), it can be considered a key element of a beautiful wedding novel. Their love should be something that readers can feel deeply.
Well - developed characters are also important. If the characters in the novel are multi - dimensional and their growth is related to their love story and the upcoming wedding. For instance, in a novel where a shy girl becomes more confident because of her love and looks forward to her wedding with new - found courage. This kind of character development adds to the beauty of a wedding novel.
The description of the wedding itself. If the author can vividly describe the setting, the emotions of the characters, and all the little details like the flowers, the dress, and the vows. In 'The Wedding' by Nicholas Sparks, he does a great job in making the wedding scene come alive, which makes the novel beautiful in terms of the wedding aspect.