As liberal theology diverged from protestantism in the 19th century, it created a crises of authority with Christianity in America. The squabbling over orthodoxy led to theological innovation, which diminished the authority of Scripture, spurred dogmatic doctrinal claims, and revised Christianity with modernism. As the Unitarians such as William Ellery Channing arrived on the scene, later men like Henry Bushnell, often called the father of American liberal theology, would cast a different vision for Christianity. The birth of theological liberalism developed into the prominent social gospel movement of the early 20th century. Gary Dorrien, in his excellent three volume work, The Making of American Liberal Theology, argues that the main premise upon liberal theology is the conviction that Christianity can be expressed without reliance upon an external authority. As enlightenment thinkers probed the Scripture with a critical eye, scholars began to question the veracity of the Bible. Under this pressure, liberalism developed as a third way alternative "between the authority-based orthodoxies of traditional Christianity and the spiritless materialism of modern atheism or deism" (Dorrien, 1:xiii).
This epistemological shift from the authority of Scripture to modernistic rationalism and romantic existentialism brewed tensions between those committed to orthodoxy and those committed to revising Christianity. Both the conservatives and the liberals within the Christian church believed they were protecting the church from the tumultuous shift of modernism. Conservatives resisted the philosophical shift taking place all around them, attempting to use reason to defend their belief in the authority of Scripture and protestant orthodoxy. The liberals attempted to recast Christianity in modern light, in attempts to keep it relevant in a culture that was becoming critical and skeptical about religious claims. All of this came to a head in the fundamentalist-modernist controversy of the 1920s and 30s.
J. Gresham Machen argued in his book Christianity and Liberalism that Christianity and liberalism are not two variations of the same religion, but two entirely different religions, built on two very different foundations. This is the tragic irony of liberal theology, in attempts to shed away the external authority of the Bible they only replaced it with a wobbling authority of ever changing cultural ideals. They've taken the firm foundation of the word of Christ and replaced it with the shifting sands of contemporary cultural whims.
As time has proven, theological liberalism is a failed project. As many mainline, liberal denominations fade into obscurity as their numbers dwindle, we must be reminded of the importance of the authority of Scripture in the Christian church. If the word of God is not the authority, something else will take its place, to the decline and distortion of the church. No third way exists between Christ and the world. The Gospel has always offended popular culture and any attempt to dilute its offensiveness only leads to ruin. As voices within and outside the church continue to urge evangelicals to let go of our authority and trust in the Bible, may we cling ever tighter to the unchanging word of God.