Quote 1
"Pleasure is the only thing worth having a theory about," he answered in his slow melodious voice. "But I am afraid I cannot claim my theory as my own. It belongs to Nature, not to me. Pleasure is Nature's test, her sign of approval. When we are happy, we are always good, but when we are good, we are not always happy."
"Ah! but what do you mean by good?" cried Basil Hallward.
"Yes," echoed Dorian, leaning back in his chair and looking at Lord Henry over the heavy clusters of purple-lipped irises that stood in the centre of the table, "what do you mean by good, Harry?"
"To be good is to be in harmony with one's self," he replied, touching the thin stem of his glass with his pale, fine-pointed fingers. "Discord is to be forced to be in harmony with others. One's own life – that is the important thing. As for the lives of one's neighbours, if one wishes to be a prig or a Puritan, one can flaunt one's moral views about them, but they are not one's concern. Besides, individualism has really the higher aim. Modern morality consists in accepting the standard of one's age. I consider that for any man of culture to accept the standard of his age is a form of the grossest immorality."
"But, surely, if one lives merely for one's self, Harry, one pays a terrible price for doing so?" suggested the painter.
"Yes, we are overcharged for everything nowadays. I should fancy that the real tragedy of the poor is that they can afford nothing but self-denial. Beautiful sins, like beautiful things, are the privilege of the rich." (6.8)
Basically, Lord Henry seems to think that if you can afford to be sinfully self-indulgent, you should go ahead and do it. His vision of good and evil is a rather cloudy one – to him, the real conflict is between the self and the society that surrounds it. See also "Morality and Ethics" for more on Henry's views.
Quote 2
He shuddered, and for a moment he regretted that he had not told Basil the true reason why he had wished to hide the picture away. Basil would have helped him to resist Lord Henry's influence, and the still more poisonous influences that came from his own temperament. The love that he bore him -- for it was really love -- had nothing in it that was not noble and intellectual. It was not that mere physical admiration of beauty that is born of the senses and that dies when the senses tire. It was such love as Michelangelo had known, and Montaigne, and Winckelmann, and Shakespeare himself. Yes, Basil could have saved him. But it was too late now. The past could always be annihilated. Regret, denial, or forgetfulness could do that. But the future was inevitable. There were passions in him that would find their terrible outlet, dreams that would make the shadow of their evil real. (10.7)
Lord Henry's triumph is apparent here. Basil, who represents all that's good and loving, is ousted by the influences of both Lord Henry and Dorian himself. It looks for the moment like the struggle is over, and evil has won.
Quote 3
Yes, he was certainly wonderfully handsome, with his finely curved scarlet lips, his frank blue eyes, his crisp gold hair. There was something in his face that made one trust him at once. All the candour of youth was there, as well as all youth's passionate purity. One felt that he had kept himself unspotted from the world. No wonder Basil Hallward worshipped him. (2.2)
Youth and purity are tied inextricably here in Lord Henry's observations of Dorian; youth is clearly something to be idolized for these characters.