Why does rauschenbusch argue that the salvation of individuals is not sufficient to address social problems?

Rauschenbusch argues that individual salvation focuses on personal piety and spiritual transformation, neglecting the systemic injustice present in society. He believes that a collective salvation is necessary to address social problems, as it involves transforming not just individuals, but also institutions and structures that perpetuate inequality and suffering. Rauschenbusch's "social gospel" emphasizes the importance of both personal transformation and social reform for achieving lasting change.