In chapter two: The Gift of Communion the Holy Father elaborates further on the gift of the Apostolic Church, without which there can be no salvation. He builds on St Paul’s trinitarian blessing in the 2 Corinthians and points out that the phrase ‘in the fellowship of the Holy Spirit’ combines the intimate unity and fellowship in the Holy Trinity with the unity and fellowship Christians enjoy in the Church.

As we share in spiritual fellowship with one another we also share in the Divine Life at the heart of the Holy Trinity. This fellowship (koinonia in Greek) is not simply the earthly fellowship or goodwill we share naturally with family and friends, but a supernatural sharing in the Divine Life. 
It is a fellowship of love, but it cannot be a fellowship of love if it is not also a fellowship of Truth. The two, Love and Truth, are part of the same fellowship, and are interdependent. Love cannot be fostered and Truth cannot be guaranteed without a shared authority that focusses that Love and defines and defends the Truth. This authority is the authority of Christ which he clearly delegates to his Apostles, and from Clement of Rome in the late first century to the other Apostolic Fathers, it is clear that the apostles carefully ensured that their authority was passed on to their successors.
The fellowship we share is a sharing in the death of Christ and it is shared through the Eucharist. The bread we share is the bread of life which is the Body of Christ, and it is no co incidence that the term ‘Body of Christ’ therefore is used for both the Church and the Eucharist. As St Paul teaches, “We are all of one body for we all share in the one bread.”
Finally, it is the Holy Spirit that binds us together in this supernatural fellowship. The Holy Spirit maintains an intimate and everlasting bond with the Church–continually inspiring and enlivening her in the life of faith.
As usual, the Pope’s writings spring from a deep reading of the Scriptures, a full knowledge of the Fathers of the Church and a keen gift of teaching and communicating the faith clearly. He is good at quotable quotes, “The Church of Love is also the Church of Truth.” And a great quote from St Irenaeus, “Wherever the Church is, God’s Spirit is too; and wherever God’s Spirit is there is the Church and every grace; for the Spirit is Truth.”