This quote is said by Estella to Pip when she informs him that she is to be married to Drummle, who is described by Pip as a "brute of a man," and clearly depicted as a very unpleasant individual indeed. Note what Pip says to Estella just a few lines before Estella delivers the quote that is mentioned in this question:
Estella, dearest Estella, do not let Miss Havisham lead you into this fatal step. Put me aside for ever,—you have done so, I well know,—but bestow yourself on some worthier person than Drummle. Miss Havisham gives you to him, as the greatest slight and injury that could be done to the many far better men who admire you, and to the few who truly love you.
Pip in this quote is concerned about Estella is doing to herself by marrying Drummle. She is making a "fatal step" according to him, and he urges her to forget Drummle and marry somebody else who is "worthier" for her. Estella replies in a very ironic way. Her speech to Pip assures him that she is not the only person who will suffer as a result of her marriage to Drummle, as she will definitely not be a "blessing" in any way. She cuts through Pip's idea that it is she alone that will be hurt through this relationship and presents herself as being more than an equal of Drummle in terms of her heartlessness and strength. Pip still thinks of love in relation to marriage, and believes Estella will get hurt, whereas Estella does not associate love with marriage, and this explains the irony of her quotation.