The character of Lord Henry Wooton in The Picture of Dorian Gray serves as a rhetorical device for several reasons:
First he represent the basic Id of every human being. This basic Id means the inner cauldron of the human soul which is inherently capable of all the sins and evils possible all for he sake of experiencing new sensations, as he said himself.
Secondly, he represents the aesthetic movement and the philosophies that Wilde so much admired at the time from Walter Pater (Art for Art's sake),and the artificial creation of beauty, the exploration of the good and the bad, and the consistent seeking of pleasure.
Third, Lord Henry (or Harry) also serves as Dorian's conscience, or lack thereof. Lord Henry presented to Dorian everything Dorian always wanted to explore, all the passions, all the pleasures, and all the levels of emotion possible. Lord Henry was the snake in Paradise that engaged Dorian into the corruption of his soul. He presented to him all the possibilities in becoming amoral in which the first thing is the lack of responsibility in one's choices.
This is how Lord Henry is a representation of sin, temptation, and corruption in Dorian's life.