The paper is divided in two parts. The first presents my exegesis of the fourth chapter of the Gospel of John. My main claim is that the composer of the text manipulate the chronological order of miracles in his "signs source" in order to approach the story of the woman from Samaria together to the healing of the son of the roman officer in Kapharnaus. The two episodes deal with two different ways to convert to faith. Consequently, they provide a complete phenomenology of the formation process of religious belief. The second part considers two fundamental interpretations of the johannine notion of faith, i.e. the fideistical and the existentialist. I reject both: the first is logically inconsistent within the Johannine framework (the Gospel of John assumes principles whose consequences contradict the fideistic interpretation of faith); the second is ontologically senseless.