Nowadays most churches would be incorporated, that means that you would register your church with a state which creates a legal organisation, as defined and regulated in law, with legal personality, which is empowered to buy and own property. Who does the church building and its bank accounts belong to? The legal corporation as recognised and created by the state, it doesn’t belong to any individual person, it is owned by a legal fiction as it were. Despite constitutional language to the contrary, the state does in fact establish the legal personality and basis for churches.
Consider the alternative. A group of people wants to form a church, it wants to have a building to worship in, a collective fund to fund its charitable activities then we return to the same question: who shall own the building and funds? In place of a legal entity, the alternative would be a private individual, the church can pool the money and then commit it to a single private individual who will purchase the building in his name, and deposit the money in a bank account of his own. Remember, before the days of legal incorporation Judas was entrusted with the money bag, perhaps not the most auspicious of portents for the future of simply entrusting church money with a single individual.
The problem naturally is that all the churches resources would be literally under the sole control of a single person. If he decides to apostasise, or if he dies suddenly and fails to make provisions for the passing on of the churches’ assets to another member of the church, all the church’s property would simply disappear from the use of the members of the church. (This is not even accounting for the problem of fraud or embezzlement as obviously this private person does not need to be audited.) It seems as such too much of a risk to entrust all of the church’s property in the hands of one man.
An alternative solution would be to nominally make a person the owner of the church’s property but to be held in trust for the church’s use. A lot of churches and their property in Europe are still held on his basis, an individual has nominal ownership but the monies are held in a trust to be used for the benefit of the church. The problem with this however is that usage of a property held in trust is still ultimately under the jurisdiction of the courts, and it is for the court to scrutinise and determine whether or not the church funds has been used for the purpose for which it is entrusted. We need not dwell too long as such on this option as the problem is structurally the same as legal incorporation.
This little discussion on the legal basis for church ownership of property is a good launching pad for the origins of church establishment. If a king or emperor wanted to patronise or found a church, what would he do? He would have a church built with his own money and his own wealth, and the church would literally be under his name and be his own property. Many churches as such sprang up under the same conditions, building built and endowed by aristocrats and nobles, the church was literally their private property. Overtime, either the central royal governments absorbed these churches, or upon the death of the founding nobility, their wills stipulated that the use of the property will be held in trust for the benefit of the church.
The reality however is that once a church reaches a certain scale or size, unless they want to literally entrust their vast wealth and resources into the hands of a single private individual, church incorporation or trust is inevitable, and inevitably, the state will be involved in regulating, managing, and adjudicating the use of such monies. Religious establishment as such is inevitable and simply cannot be avoided.