The Christian faith as a possibility of a real human existence, seeks to make a reading of the theological thought of Joseph Ratzinger, systematizing the set of themes of Christian faith and demonstrating the strength and vitality that make it, currently, a possibility of human existence. The scenario that makes background to this study is the question of truth and the crisis of faith in the modern context. Given the current cultural and theological circumstances of the Christian faith, Christianity faces a real dilemma: the modern understanding of reality, in which the cognoscitive scope is limited to sensitive, phenomenal, where the only reality that exists is the matter establishing, thus, a reign of feasible and the prevalence of a philosophy: relativism. The Christian faith, however, goes beyond what pure reason is capable of recognizing, towards Christ, the logos, the sense, the truth itself. The human being can not be sustained only by what is visible, tangible and measurable, so faith impels a person to a decisive opening to the Logos. Therefore, the Christian faith is not a system, an idea, a blind surrender to the irrational, but it belongs to the realm of truth, it is the choice for the priority of reason and rational. Believing is reasonable. Thus, it is possible to understand the humanizing function of the Christian faith and its personal structure: the essence of the Christian faith is to accept and live life as relationality, whose core formula is I believe in You and not I believe in something. In this relationship with God Person is established the primacy of love: being a Christian is to humanize by love. A God-Love that acts so transtemporal and trans-local, promoting an encounter of faith with cultures, not to deprive them of something, rather to provide a stimulus to search for the fullness of truth. This synthesis of thought of Ratzinger about the Christian faith wants to assert that only in God, the human being attains the meaning of life, a real and true human existence.