It is no mistake that this same Upper Room was the place where the Holy Eucharist was instituted, and where, by virtue of his command that they ‘do this in remembrance’ the Apostles were ordained and had bestowed upon them the priesthood of Christ. This same Upper Room where the Eucharist was established is also the location for the descent of the Holy Spirit. The five can therefore never be separated: The Holy Spirit, the Mystical body of Christ the Church, the Mother of God, the Eucharist and the Apostolic Authority. The five come together in the painting as the central feature is a large and permanent altar, on which the Mother of God stands and around which the apostles circle.
The Upper Room is painted as an exalted building with classical columns and an overarching ceiling which is open to heaven itself. This place is a Bethel–a threshold of heaven–the doorstep of transcendent glory. The place where the Holy Spirit descends is therefore shown to be the Church–empowered and strengthened by the pillars which are the apostolic authority and at her center the Mother of God who is also the Mother of Christ and therefore the Mother of the Church.
That this room is a solid, classical structure with columns, floor and altar and ceiling reminds the viewer that the Church is a temple and that the members of the church are living stones. It also reminds the viewer that the Church is not an invisible and spiritual reality alone, but it is a solid, historical, tangible reality. The Church, like the Body of Christ, is real. It is identifiable in history. It has a definable set of dogmatic beliefs and moral teachings. It also has a structure, a hierarchy, a code of law, and a system of governance and authority. It is something solid and substantial and historical.
All of this, we believe, was founded and continues to be inspired and filled with the power of the Holy Spirit. Individual experiences of the Holy Spirit are a good thing. However, Catholics recognize that on their own, they are ephemeral, subjective and unreliable. How do we know that what a person says is the Holy Spirit is indeed the Holy Spirit? As C.S.Lewis said, that ‘religious experience’ may simply be the result of a very good dinner. Likewise it may be an ordinary human psychic or emotional experience. It may be something manufactured by a blend of powerful oratory, emotional music and feelings of guilt or exaltation. It may even be the manifestation of disordered and evil spiritual entities.
The individual experience of religion therefore needs to be grounded in the objective experience of the Church. It is only within the Church that our individual experience can be validated, and it is only a Church with a reliable, historic, Scriptural, rational, Apostolic authority which can speak with the necessary authority to validate the subjective experience.
This is the church we see being established at Pentecost, and this is the Church which subsists today in the Roman Catholic Church.