Willa learns to see people like her Latino neighbors (whom she looked down on in a way, not with active racism but with a sense of superiority) in a new light, as good people she could learn from. Tig challenges Willa's thwarted liberal expectations of the "good life" and her resentment that she and her husband, despite being good citizens and smart professionals, can barely make ends meet. They've been cheated by economic change. All that is true, Tig points out, but the rules have changed for everyone, even for folks who've never shared her relative privilege and expectations. And Tig pushes her to realize that "things," even nice houses, are ultimately not what matters, in the face of the threat to survival on the planet. Tig's "secret of happiness" is that people matter most, that attachment to objects is a waste of our time. Instead, building a community, sharing and recycling resources, being creative and taking gratitude and enjoyment from something as simple as a good meal, is ultimately as necessary as it is fulfilling.
Later, while clearing out her accumulations of "stuff," Willa finds a quote on happiness that her mother had copied from Willa Cather, to be read at her funeral, but Willa had mislaid and forgotten about it. The quote talks of happiness as being like pumpkins or people soaking up sunshine, a sense of being "dissolved into something complete and great." The quote makes a powerful emotional impact on Willa; in a way, it expresses the new understanding she's developed from her conversations with Tig: that her real happiness is not dependent upon a fancy house, but on the way her relationships and her expanding family, including Tig's partner, the Hispanic neighbor Jorge, are growing into something "complete and great," along with a new sense of needing to become part of a broader community for the sake of future generations. I think that's also Kingsolver's message for us: to value our common humanity, across ethnic differences, and to value our relationship to the earth itself, and work together to make the changes necessary for survival.