Why is Elizabeth pleased when Mr.Darcy enters into a conversation with the Gardiners?

Elizabeth was pleased that Darcy had met and was happily conversing with her Aunt and Uncle. Because of their conversation, Elizabeth understands that Darcy is open to moral hierarchy, which is in fact more important than the social hierarchy which might have kept him from engaging the couple in conversation.

“Elizabeth could not but be pleased, could not but triumph. It was consoling, that he should know she had some relations for whom there was no need to blush. She … gloried in every expression, every sentence of her uncle, which marked his intelligence, his taste, or his good manners” (255).