Walter Rauschenbusch is known as the father of the Social Concern movement in America. Traditionally, the source of his social ethic has been seen to lie in the single motif of liberalism. Donovan Smucker provides a new perspective, arguing that Rauschenbusch's social ethic was based on not one but four complementary influences: pietism, sectarianism, liberalism, and transformationism.

In Rauschenbusch's work pietism, a religion of the heart, was purged of subjectivism while retaining inter-personal compassion; Anabaptist sectarianism provided a Kingdom of God love-ethic without passivity toward the culture; liberalism imparted an openness to the whole community and a powerful, realistic analytic; and the transformationist Christian socialists supplied a case for state intervention while rejecting public ownership as a first principle. Smucker reveals that while the roots of Rauschenbusch's new paradigm lay to some extent in his personal experiences his parents' rejection of the Lutheran perspective for that of the Baptists, his father's pietism, and his eleven-year pastorate in New York's Hell's Kitchen it was his exposure to the new politics of Henry George and Edward Bellamy, to the Christian socialism of England and Switzerland, and, aided by his knowledge of German and his experiences in Europe, to a wide range of scholarship sensitive to the main social currents of the day that deeply informed his ethic. Smucker also shows how Rauschenbusch drew upon the work of Christian ethicists, historians, and sociologists to support his new pluralistic synthesis.