The existentialism we see today is rooted most prominently in the writings of Søren Kierkegaard, and as a consequence, it might be argued that modern existentialism started out as being fundamentally Christian in nature, only later diverging into other forms. It is thus important to understand Christian existentialism in order to understand existentialism at all.

A central question in Kierkegaard’s writings is how the individual human being can come to terms with their own existence, for it is that existence which is the most important thing in every person’s life. Unfortunately, we are as if adrift in a infinite sea of possible modes of living with no secure anchor that reason informs us will provide certainty and confidence.

This produces despair and anguish, but in the midst of our “metaphysical sickness” we will face a “crisis,” a crisis which reason and rationality cannot decide. We are forced to reach a decision anyway and to make a commitment, but only after making what Kierkegaard called a “leap of faith” — a leap that is preceded by an awareness of our own freedom and the fact that we might choose wrongly, but nevertheless we must make a choice if we are to truly live.

Those who have developed the Christian themes of Kierkegaard’s existentialism explicitly focus upon the idea that the leap of faith we make must be one which causes us to surrender ourselves totally to God rather than to insist on a continued reliance upon our own reason. It is, then, a focus upon the triumph of faith over philosophy or intellect.

We can see this perspective most clearly in the writings of Karl Barth, a Protestant theologian who was among the most faithful to Kierkegaard’s religious intentions and who can be looked upon as the starting point of explicitly Christian existentialism in the twentieth century. According to Barth, who repudiated the liberal theology of his youth on account of the experiences of World War I, the anguish and despair we experience in the midst of an existential crisis reveals to us the reality of the infinite God.

This is not the God of the philosophers or of rationalism, because Barth felt that rationalistic systems of understanding God and humanity had been invalidated by the destruction of the war, but the God of Abraham and Isaac and the God who spoke to the prophets of ancient Israel. Neither rational grounds for theology nor for understanding divine revelation should be sought after because they simply don’t exist. On this point Barth relied on Dostoyevsky as well as Kierkegaard, and from Dostoyevsky he drew the idea that life wasn’t nearly as predictable, orderly, and reliable as it appeared to be.

Paul Tillich was one Christian theologian who made extensive use of existentialist ideas, but in his case he relied more upon Martin Heidegger than Søren Kierkegaard. For example, Tillich used Heidegger’s concept of “Being,” but unlike Heidegger he argued that God is “Being-itself,” which is to say our ability to overcome doubt and anxiety in order to make the necessary choices to commit ourselves to a way of living.

This “God” is not the traditional God of classical, philosophical theism nor is it the God of traditional Christian theology — a sharp contrast to Barth’s position, which has been labeled “neo-orthodoxy” because of its call for us to return to a a non-rational faith. Tillich’s theological message was not about turning our lives over to the will of a divine power but rather that it is possible for us to overcome the apparent meaninglessness and emptiness of our lives. That, however, could only be achieved through what we choose to do in response to that meaninglessness.

Perhaps the most extensive developments of existentialist themes for Christian theology can be found in the work of Rudolf Bultmann, a theologian who argued that the New Testament conveys a genuinely existentialist message which has been lost and/or covered over through the years. What we need to learn from the text is the idea that we have to choose between living an “authentic” existence (where we face up to our own limits, including our mortality) and an “inauthentic” existence (where we recoil from despair and mortality).

Bultmann, like Tillich, relied heavily upon the writings of Martin Heidegger — so much so, in fact, that critics have charged that Bultmann simply portrays Jesus Christ as a precursor to Heidegger. There is some merit to this accusation. Although Bultmann argued that the choice between an authentic and inauthentic existence cannot be made on rational grounds, there there does not seem to be a strong argument for saying that this is somehow analogous to the concept of Christian grace.

Evangelical Protestantism today owes a great deal to the early developments of Christian existentialism — but probably more those of Barth than of Tillich and Bultmann. We continue to see a focus on key themes like the the emphasis of an engagement with the Bible rather than philosophers, the importance of a personal crisis with leads one to a deeper faith and personal understanding of God, and valuation of irrational faith over and above any attempt to understand God through reason or intellect.

This is a rather ironic situation because existentialism is most often associated with atheism and nihilism, two positions which are common excoriated by evangelicals. They simply don’t realize that they share more in common with at least some atheists and atheistic existentialists than they realize — a problem that might be corrected if they were to take the time to study the history of existentialism more closely.