The church owns an enormous amount of property. Its buildings cost millions and are used for a few hours a week, and their upkeep comes out of budgets that are themselves a large fraction of what members give. Ask what justifies the sums, and the answers are usually about worship, or witness, or the needs of the congregation.
The fourth century gives a sharper answer, because it produced two buildings in one lifetime and they point in opposite directions.
Constantine's building
The first is the basilica, the Roman civic hall that Constantine gave the church. It had a long nave and side aisles, and at the end a raised apse where the magistrate had sat and the bishop now sat. Its purpose was to hold a large audience facing one direction, listening to one voice. It was, and is, a superb machine for producing spectators.
The basilica was justified by what happened on Sunday. It was full then and empty otherwise. It also established the principle that has governed church buildings ever since, that a building exists for the gathering and the gathering is the audience.
Basil's building
The second was built by Basil of Caesarea, a bishop in what's now central Turkey, a few decades after Constantine. He built a complex outside the city, far more than a hall, and the people called it the Basiliad. It consisted of a hospital, a hostel for travelers, a poorhouse, workshops where the unemployed could learn trades, and a colony for lepers whom Basil himself is recorded as having tended with his own hands.
Basil's building was justified by what happened on Tuesday. It was busiest when there was no service. Its purpose was what it did for people who weren't members, for the sick, the stranger, the poor, the unemployed and the leper. It was the first institution of its kind in the history of the world; the hospital as we know it descends from it.
A hostile witness named the mechanism. The pagan emperor Julian, trying to revive the old religion, complained bitterly in a letter to one of his priests that the Christians' care for strangers (their poor and ours) was what made their religion attractive, and he ordered his priests to copy it.
Both buildings were raised by Christians in the same century. The basilica borrowed from Rome and made the church an audience, while Basil's answered the gospel and made the church a hospital.
What Scripture says a building is for
The New Testament has almost nothing to say about church buildings, because it had none. But it has a great deal to say about what the church's resources are for.
For I was an hungred, and ye gave me meat: I was thirsty, and ye gave me drink: I was a stranger, and ye took me in: Naked, and ye clothed me: I was sick, and ye visited me: I was in prison, and ye came unto me... Verily I say unto you, Inasmuch as ye have done it unto one of the least of these my brethren, ye have done it unto me. (Matthew 25:35-40)
Set that list of the hungry, the thirsty, the stranger, the naked, the sick and the imprisoned beside the Basiliad, with its hospital, hostel, poorhouse and workshops. Basil built Matthew 25 in stone.
Pure religion and undefiled before God and the Father is this, To visit the fatherless and widows in their affliction, and to keep himself unspotted from the world. (James 1:27)
James defines religion, meaning the outward practice of faith, by two things. The first is care for those without protection.
Is not this the fast that I have chosen? to loose the bands of wickedness, to undo the heavy burdens, and to let the oppressed go free, and that ye break every yoke? Is it not to deal thy bread to the hungry, and that thou bring the poor that are cast out to thy house? when thou seest the naked, that thou cover him... And they that shall be of thee shall build the old waste places: thou shalt raise up the foundations of many generations; and thou shalt be called, The repairer of the breach, The restorer of paths to dwell in. (Isaiah 58:6-7, 12)
Bring the poor that are cast out to thy house. The house is for the outsider. The promise attached is a building promise (build the old waste places, raise up the foundations), and in it the building comes after the feeding.
Acts gives the earliest description of what the church did with its money.
Neither was there any among them that lacked: for as many as were possessors of lands or houses sold them, and brought the prices of the things that were sold, and laid them down at the apostles' feet: and distribution was made unto every man according as he had need. (Acts 4:34-35)
Instead of acquiring property to house a service, the first Christian capital campaign liquidated property to feed the poor.
Two criteria for any building
From the two fourth-century buildings and the texts, two criteria follow for any building a congregation owns.
The first is whether non-members use it. A building justified by what it does for the people who already belong is a clubhouse, and one justified by what it does for the sick, the stranger, and the poor is a Basiliad. Because the design's outward purpose is that election is for the outsider, the building's purpose is measured outside the membership.
The second is whether it's busier on Tuesday than on Sunday. A building that fills for the gathering and empties otherwise is an auditorium. If the gathering is one use among many, and not the largest, the building is doing what Basil's did.
A third follows from those two. Design for Tuesday. When a congregation is going to build or renovate, the question is what the building does at ten o'clock on a weekday morning, and for whom. How many the sanctuary seats is the wrong question.
What this looks like
In practice it means rooms handed over free of rent to the things the neighborhood needs. A food distribution can run from the kitchen, and a clinic, or the space for one, can take a room. Tutoring can go on in the classrooms that sit empty six days, and the parsonage nobody lives in can house those who need it. There can be a workshop, a laundry, and a place to charge a phone and be warm. There can be recovery meetings, the church's own and other people's, and a meal every week for anyone.
None of this is new. It's what the Basiliad did with fourth-century means. None of it competes with the church's mission either, because a building that houses the destinations is not a competing destination. It's the place where the Matthew 25 list gets done, and where the neighbor, who will never attend a service, meets the people who serve.
The plainest rule is to stop charging rent and call it the ministry. A congregation that leases its rooms to community groups at market rates has a landlord's relationship to its neighbors. One that gives the rooms away has Basil's.
The cautions
I'll give six, briefly. A building can become the ministry's excuse, so that the people serve the building instead of the neighbor. Institutional charity can substitute for personal contact until the poor are fed and never known. Doing good can license neglect elsewhere, as in the congregation that runs a food bank and has no one-anothers. Safeguarding isn't optional. Vulnerable people in a building require real protections. Mission-drift is real, and a church that becomes a social agency has lost the thing that made Basil's charity different from the emperor's. Last, the members must do the work themselves, because work outsourced to staff stops forming anyone.
The practical route
Most congregations won't build a Basiliad. But every congregation with a building can ask the two questions honestly and begin moving the answers.
Count the hours the building is used, and by whom. Find the largest empty block and give it to the neighborhood's most obvious need. Stop charging for it. Staff the rooms with members and skip the paid coordinator. In a year, count again.
The fourth century offered the church two models and it took the wrong one. The right one is still there, in a letter from a hostile emperor who couldn't compete with it, and in a list of six needs that a bishop turned into a building. The sums are justified by the sentence Basil built in stone. Inasmuch as ye have done it unto one of the least of these.