Benedict XVI, in his work Jesus of Nazareth: From the Entrance into Jerusalem to the Resurrection , published in 2011, stated that the preposition for is the key word to understand the mystery of Christ and the meaning of following him, as it introduces the concept of pro-existence into theology. This present thesis aims to study how it appears and what place the concept of pro-existence occupies in the Christological work of Joseph Ratzinger. Structured in four explanatory chapters, this research proposes several preliminary considerations in the First Chapter. In the Second one, the survey exposes the manifestation of God as pro-existing throughout history. In the Third Chapter, the foundations of pro-existence are summarized on Jesus and his revelation, in the Trinitarian mystery. The Last Chapter presents the pro-existence in the sacrifice offered by Jesus on the cross. The suggested path underlies the claims of Jesus of Nazareth . The biblical term for leads the concept of pro-existence into theology: Jesus life was distinguished as an existence all engaged towards the Father and lived for the salvation of mankind. From the revelation of Jesus Christ, one is led to know the intra-Trinitarian pro-existence, and, at the same time, to consider the pro-existence of man as a person and a Christian. The height of Christ s surrender to the Father and to humanity took place in the mystery of the cross. Since Christ is the constituent element of the Christian being, one will find oneself and one s own salvation in responding to Christ s saving offer on the cross. In a concrete way, the human being will discover oneself and be saved by reproducing in a fundamental attitude that characterized the person and behavior of Jesus: living in a pro-existing way his confident and obedient surrender to the Father, and, at the same time, a solicitous love towards others.