Was it an ordinary living chamber, where people spend day and night? The very number of those presented as staying in this upper room does not allow us to think so.
Could it be fitting, convenient, or possible for the twelve apostles, the Most Holy Mother of the Lord, the myrrh-bearing women and other pious women, and the other disciples of the Lord to live in one upper room?
The Evangelist counts them all as "about one hundred and twenty names together" (Acts 1:16).
What, then, was this upper room? It reminds me of the "large furnished upper room" mentioned by the same Evangelist, concerning which the Lord said to Peter and John: "There prepare" the Passover (Lk. 22:12).
In it He established and for the first time celebrated the mystery of His Body and Blood.
Either this is one and the same upper room in its very location, or at least the one and the other are alike in purpose and dignity.
Its purpose was not that people spend day and night there, dine and sup, sit and rest. Rather, those who stayed in it "continued with one accord in prayer and supplication."
In it the Lord's Mystical Supper was celebrated. In it the election of Matthias to sacred ministry took place, and his numbering among the apostolic company.
This was an "upper room" that rose "above" all earthly and worldly things. By the pious spirit of those dwelling in it, it touched the heavenly and divine.
Therefore it finally received the highest privilege: in it heaven and the Godhead were solemnly and wondrously manifested.
The Holy Spirit not only animated the apostles by His almighty breath. He not only enlightened their minds with fiery tongues, inflamed their hearts, and formed their tongues for the worldwide preaching of salvation.
He also filled the very place of their dwelling with His holiness and grace: "It filled the whole house where they were sitting" (Acts 2:2).
Again I ask: what is this upper room? I hope that what I have said until now is enough to justify the final answer which I give to the proposed question.
The upper room of Zion, the apostolic upper room of the descent of the Holy Spirit, is nothing other than the first image of the holy Christian temple.
Conversely, the holy Christian temple, and therefore the temple now consecrated, is the apostolic upper room of the descent of the Holy Spirit repeated, renewed, and multiplied.