In his book, The Mass: The Presence of the Sacrifice of the Cross, Charles Cardinal Journet provides a following insight into the question: What is a church building?
“Still more than the house of the Christian people, the church is the house of Christ. A mystery, a presence, fills even the poorest of the Catholic churches.
The church is inhabited.
It does not live primarily by the motion of the comings-and-goings, which the crowds bring to it. A church is, rather, the very source of life and purity for those who enter within its walls. It possesses a real presence, the corporal presence of Christ, where Love Supreme touched our human nature in order to contract an eternal wedding with it, the hearth of a radiance capable of illumining the entire drama of time and human affairs.
Everyone can enter in and personally encounter the Jesus of the Gospel.
Everyone, no matter how ignorant they might be, and even though the memory of whose faults and whose secret interior trials can be overwhelming – everyone can dare to approach, as did the sinful woman in the house of Simon the Pharisee. Everyone can cry out to him, as did the blind man from Jericho: “Lord, that I might see!”
When an honest man asks us what he must do to find the Truth, before being able to explain to him the Christian catechism and mysteries, before also throwing him into the crowd of believers, where he will feel strange and where the Church which he does not yet know might appear to him to be equal to all others – before all this, we can ask him to go and sit awhile each day in an empty church, just him and the Gospel.
Later, when he understands that the Real Presence is the raison d’être of the Church’s permanence in space and time until the end of the world,
then his eyes will open to the Catholicity of the mystery of the Church, and her most humble attempts to gather men around Christ will become clear to him” (238).
“The best way for the Church to know so intensely that the mystery of the bloody Cross exists in order to open up to the mystery of glory is by contemplating the glorious Christ under the symbol of His Passion, as He dwells in our tabernacles” (210).