|Pope Benedict gives his Pentecost homily (May 11, 2008)|
"Where the Church is, there is the Spirit of God, and where the Spirit of God is, there is the Church and every grace, and the Spirit is truth; to distance yourself from the Church is to reject the Spirit" and thus "to exclude yourself from life" (Adv. Haer. III, 24, 1).
That is the antidote to Montanistic conceptions of the Holy Spirit's activity that conceptually separate the Spirit from the visible Church and from the sacraments, or redefine the Church into an invisible entity such that the 'Church' just is (by definition) whoever has the same spiritual/subjective experience and resulting belief that 'I' have.
Concerning the unity of the Church, Pope Benedict said the following in his homily:
"The Catholic Church is therefore not a federation of churches, but a single reality: The universal Church has ontological priority. A community that is not catholic in this sense would not even be a Church."
Packed into those two sentences is the ecclesiological key to achieving full visible unity. The Catholic Church that Christ founded is not a mere plurality, set, aggregate or collection of 'parts', whether they be individual persons, particular Churches (e.g. the Church at Jerusalem, or the Church at Antioch), or denominations. Christ founded an ontological reality, a *universal* (i.e. Catholic) Church, from which the particular Churches have their being (that is what Pope Benedict means by "ontological priority"). Here is the most fundamental difference between a bottom-up ecclesiology represented in the Tower of Babel, and a top-down ecclesiology represented by Christ breathing on His disciples, and then at Pentecost sending the Spirit down upon them as would occur at each valid ordination in succession from the Apostles.