This paper seeks to investigate the doctrine of the Church as the Mystical Body of Christ, reflecting on its origin, nature and mission in the light of Sacred Scripture, the Magisterium and the Tradition of the Church. Starting with Pauline theology, especially in the letters of Corinthians and Ephesians, it is understood that all the baptized constitute a single Body in Christ, vivified by the Holy Spirit. Some authors, such as the Church Fathers and Modern teologians, have studied this reality, specifically in the relationship between the Eucharist, ecclesial unity and participation in Christus Totus. Documents such as Mystici Corporis Christi and Lumen Gentium corroborate that the Church is at the same time visible and invisible, spiritual, hierarchical and charismatic. The unity and sanctification of the Mystical Body occur through the grace communicated in the sacraments, with emphasis on Baptism and the Eucharist.