In Chapter Four, when Dorian first reveals his love for Sibyl, it is clear that what has driven this infatuation is Sibyl's art as an actress. In a novel that is dominated so much by art in all of its various forms, and which sets art off against reality, Sibyl as a character represents art in all of its passionate excess. Note what Dorian says to Lord Henry about why he loves her:
Harry, I do love her. She is everything to me in life. Night after night I go to see her play. One evening she is Rosalind, and the next evening she is Imogen. I have seen her die in the gloom of an Italian tomb, sucking the poison from her lover's lips. I have watched her wandering through the forests of Arden, disguised as a pretty boy in hose and doublet and dainty cap. She has been mad, and has come into the presence of a guilty king, and given him rue to wear, and bitter herbs to taste of. She has been innocent, and the black hands of jealousy have crushed her reed-like throat. I have seen her in every age and in every costume. Ordinary women never appear to one's imagination.
We can thus see that what draws Dorian to Sibyl is her character-changing properties and her skill as an actor. Through these factors, she is able to appeal to his imagination and is a mystery to him. Of course, ironically, it is when she loses her artistic skill because of her love for him, exchanging reality for art that he is revolted by her.