Kierkegaard described human existence as three different levels: sensibility, rationality and religion. Emotional people are hedonists, or people who are keen on life experience. They are subjective and creative, have no commitment and responsibility to the world, and feel that the world is full of possibilities. Rational people are realistic, full of commitment and responsibility to the world, and have a clear understanding of the moral and ethical rules in the world. Therefore, unlike emotional people, rational people know that the world is full of limitations and impossibilities. Faced with the impossible, rational people have to give up and grieve for what they have lost forever. At this time, people only rely on "leap of faith" to enter religion, believing that everything is possible in an infinite God; Although rationally aware of the impossibility of things, it is precisely because of the absurdity of belief that people can regain hope.

In fear and trembling, Kierkegaard pondered the story of Abraham, the "father of faith" in the Old Testament. He followed God's instructions and killed his son as a burnt offering. He believes that if Abraham doesn't care about his son's life and death, there is no moral and even family psychological struggle, or he thinks that obeying God to kill his son is a moral rule, then everything he does is meaningless. The value of Abraham's action lies in his leap from rationality to religion. He believes in the power of God, absurdity, and that everything is possible and miracles will happen (as a result, God sent an angel at the last minute to stop Abraham from killing his son). Kierkegaard believes that there is no faith without reason.