In the book The Concept of Anxiety, Kierkegaard begins his study with the Bible and discovers that anxiety is the premise of sin, which is proved by the emotional experience of Adam to nothing. By means of the disclosing of the occurrence of anxiety, Kierkegaard connects anxiety with the history of human beings, so that anxiety was shown up as the original power. Furthermore, Kierkegaard also connects anxiety with sin, so the concept of God becomes the premise of his study to anxiety in which it opens a way connecting the spirit of human beings with the limitlessness and eternity. In front of God, spirit is still free but the possibility of freedom causes great anxiety. Therefore, Kierkegaard concludes that anxiety is "the dizziness of freedom" and "the entangled freedom". In this way, Kierkegaard extends anxiety from physiological categories to philosophical domain. Anxiety becomes a philosophical concept describing the existing conditions of humankind.