Religious beliefs are, after all, beliefs, not objective bits of knowledge. But only the religious life is truly authentic. Rationality and knowledge are based on the premise that truth is objective, impersonal, a relationship between a belief and the world. This means that authentic existence requires from us a leap of faith. Only a leap of faith can surmount the gap.
Moral knowledge is general, faith in salvation is particular.
The leap of faith is not irrational as much as beyond rationality. Abraham in the Old Testament is a classic example of the person of faith. For Kierkegaard, he is the embodiment of the religious mentality. By taking responsibility for one's actions and affirming one's power, the authentic individual exhibits the kind of faith and commitment that provides no guarantees or proofs. In the end, religious belief thus boils down to an attitude that is unjustifiable.