As a potential minister, he was more determined than ever to be like Benjamin Mays and serve God and humanity from his pulpit. As a consequence, King was not content simply to follow Crozer's prescribed course of study. On his own, he began a serious quest for a philosophical method to eliminate social evil, a quest that sent him poring over the works of the great social philosophers, "from Plato to Aristotle," as he wrote later, "down to Rousseau, Hobbes, Bentham, Mill and Locke."
While he gained something from each of these thinkers, it was the theologian Walter Rauschenbusch who initially influenced him the most. In the turbulent 1890s, this tall, deaf, bearded scholar had taught church history at Rochester Theological Seminary, embroiled in ecclesiastical controversies of a bygone industrial America. Beyond his study, a Social Gospel movement blazed in industrial America, as modernist Christians attacked the evils of unbridled capitalism and sought to make their religion relevant to the problems of the modern world. As the new century dawned, educated young clergymen across America demanded that social justice be defined in Christian terms.
Swept up in this tempest of reform, Rauschenbush abandoned recondite scholarship and became the leading prophet of the new Social Gospel. In Christianity and the Social Crisis and other impassioned books, he blamed capitalism for all the squalor and want that plagued the land. Damning business as "the last entrenchment of autocracy," capitalism as "a mammonistic organization with which Christianity can never be content," Rauschenbusch summoned Christians to build a new social order - a true Christian commonwealth - in which moral law would replace Darwin's law of the jungle. Such a commonwealth had been the original mission of Christianity, Rauschenbusch contended, since Christ had called for a kingdom of God on earth, a whole way of life dedicated to the moral reconstruction of society. Theologians and ecclesiastics, however, had misconstrued Christ's teachings and founded not a kingdom but a church, which then amassed interests of its own. But what really shattered Christ's dream was the industrial revolution, which spawned capitalism and a whole era of competition, greed, and plunder. Still, Rauschenbusch did not attribute such evil to man himself, for man was basically good, intrinsically perfectible, able to become like Christ. No, sin was the product of an evil society - in this case, capitalist society. Exploitation, prostitution, crime - all were inherent in a social system that exalted profit over virtue, selfishness over brotherhood. The time had come, Rauschenbusch asserted, for Christians to eradicate capitalism, socialize vital economic resources, and establish God's kingdom as Christ originally intended. The time had come to usher in "the glad tomorrow," when man would inhabit a sinless Christian commonwealth based on love, cooperation, and solidarity.
At Crozer, King read Rauschenbusch in a state of high excitement. Here was the Christian activism he longed for. While he though Rauschenbusch perilously close to equating God's kingdom with a specific social and economic system, which no Christian should ever do, King nevertheless became an ardent disciple. As he said later, Rauschenbusch provided him with a theological foundation for social concerns he'd had since he was a boy. And he engaged in spiritual debates with anybody - professor and preachers alike - who held that man had only a limited capacity for improvement and that the church should confine itself to matters of the soul. A socially relevant faith must deal with the whole man - his body and soul, his material and spiritual well-being. It must work for the kingdom "down here" as well as "over yonder." Any religion that stressed only the souls of men and not their social and economic conditions was "a spiritually moribund religion awaiting burial."
-pg. 24-25 of Let the Trumpet Sound: The Life of Martin Luther King, Jr. by Stephen B. Oates