The title comes from a line in the Hebrew Bible, Ecclesiastes 7:4 to be more specific: "The heart of the wise is in the house of mourning; but the heart of fools is in the house of mirth." In other words, wise people think about death and loss and other serious matters, while foolish people are busy thinking of only happy and silly things. When you read the passages surrounding 7:4, what you walk away with is some general advice to take life seriously instead of indulging in pleasure.
Remind you of anything? Another way to describe this dichotomy is to contrast "Stoic" (thinking about serious stuff) and "Epicurean" (pleasure-seeking). Lawrence Selden is at one point described as combining "the stoic's carelessness of material things […] with the Epicurean's pleasure in them." In Lily's "Character Analysis," we discuss her transformation from a material girl to a pillar of morality – in other words, she's an Epicurean-turned-Stoic.
The House of Mirth – like this passage from Ecclesiastes – praises stoicism and rejects Epicureanism. We talk in "Character Analysis" about the dichotomy of money and morality in the novel. Characters have to choose between material luxuries and goodness. Wharton makes it clear that the correct choice, in her mind and therefore in her novel, is goodness and morality – and this choice of title reinforces that bias.