All Christians suffer from unbelief. Worry and anxiety are forms of unbelief (Matthew 6:25-34; 1 Peter 5:7). But it is one thing to lapse into functional unbelief and quite another thing to integrate unbelief into your view of God. And that kind of integrated unbelief is what happened in the 18th century as Liberal Christianity (in the technical sense) began to emerge.
To understand Liberal Christianity you need to know about two thinkers of the 18th to mid-19th century: Immanuel Kant and Friedrich Schleiermacher. Both men share the same philosophical starting point; namely, that science operates on the basis of sense experience and so any metaphysical questions about God (such as his existence) are to be excluded on the basis of science. For Kant this meant that all that was left over in religion was relegated to the realm of morality; for Schleiermacher, this meant that one could accept this metaphysical predicament but then build a whole system of theology, prayer, church, etc. around the experience of “God-consciousness,” which he called a “feeling of dependence” on God.
But the problem here is that once you discard the metaphysical reality of the Triune God, you might as well be consistent and throw out all statements about God. This whole talk of “God-consciousness” or a “feeling of dependence” is a waste of time. Now of course, anyone can follow Schleiermacher and waste much time (and ink) talking about God, the Holy Spirit, and a whole manner of Christian truth, but it will always sound inconsistent; a Liberal Theology can be constructed, but only out of one side of the mouth, for the other side of the mouth completely denies any metaphysical certainty of God’s existence. That is what Karl Barth understood, and so masterfully critiqued with devastating blows.
I personally have a lot more time for a guy like Richard Dawkins than a guy like Schleiermacher. Dawkins understands that if you wipe out the metaphysical foundation for God on the basis of science then at least be consistent and throw out theology altogether! Now of course I disagree with Dawkins – I think there is metaphysical evidence for God – but I can at least appreciate his consistency.
 Gary D. Badcock, Light of Truth and Fire of Love: A Theology of the Holy Spirit (Grand Rapids, MI: Eerdmans 1997), 113-17.