This dissertation uses the case of ELIJAH, a large and diverse faith-based community organization, to advance social scientific understandings of the role of culture and emotions in social movements and progressive religious activism in twenty-first century U.S. political culture. Drawing on participant-observation and in-depth interviews, I document the ongoing construction of organizational culture and commitments to activism through a discursive practice that I call vulnerability talk. In the absence of a clear collective identity or a shared set of material interests, people in ELIJAH turn to emotions as the basis for fostering solidarity across racial and ethnic difference. This organizing paradigm shapes ELIJAH’s identity formation, narratives of action, and political strategy, and it counters dominant assumptions in the previous sociological literature on social movements, civic culture, and religion. I argue that ELIJAH’s ongoing construction of the cultural components of mobilization—collective identity, symbolic boundaries, narratives, and community bonds—produces not only activism in pursuit of social reform, but also new understandings of citizenship and religious responsibility. The importance of emotion work for managing the cultural complexities of multiracial organizing suggests that the most important question about progressive religious activism is not whether a new “Religious Left” will emerge to counter the Religious Right, but whether and how the culture being forged in progressive religious spaces can support ongoing action in the long term.