Søren Kierkegaard, often hailed as the father of existentialism, was a 19th-century Danish philosopher whose work profoundly influenced both theology and moral philosophy. He lived during the early 1800s, a time of significant intellectual upheaval in Europe, where the rise of Romanticism began to challenge the Enlightenment's rationalism. Kierkegaard’s writings emphasize the importance of individual existence, subjective experience, and the complexities of human decision-making, all of which remain relevant in modern ethical discussions.

One of Kierkegaard's most significant contributions to moral philosophy is his concept of the “leap of faith.” This is an idea that emphasizes the necessity of making a deeply personal commitment based on an understanding that transcends rationality. For Kierkegaard, moral choices are fundamentally intertwined with faith, which cannot be fully rationalized or articulated within conventional frameworks of truth. He argues that true faith—and, by extension, true morality—requires an acknowledgment of uncertainty and ambiguity; it asks individuals to move beyond merely ethical calculations and dive into the personal sphere of belief.

In his work "Fear and Trembling," Kierkegaard presents the biblical story of Abraham and Isaac as a prime illustration of his ideas. He describes Abraham’s willingness to sacrifice Isaac as an example of the “knight of faith,” someone who embodies the tension between ethical obligations and faith-based actions. The ethical demand in this narrative tells Abraham to protect his son, but his faith compels him to follow a divine command that appears unethical. This paradox is central to Kierkegaard’s philosophy and highlights the conflict often present in moral life—the clash between societal norms and personal conviction.