This Question presupposes that there is some benefit in not having Church and State separated. But, as long as there is not full and transparent separation between Church and State, there will always be the risk that the relationship will be abused for the benefit of Church or State.
It may well be that advocates of a binding relationship between Church and State expect that this would work to the benefit of the Church, but it also means that the state has the power to interfere in Church appointments, promotions and even doctrine. This Question is also pertinent to the categories in which it was asked. Outside Israel, a close relationship between religion and State could be very harmful to Judaism. Similarly, a close relationship between religion and State could be very harmful to Islam, other than in Islamic countries.
The need for a separation between church and state dates back to ancient Greece and Rome. Whether it's the trial of Socrates or the persecution of Christians, many of the world's greatest injustices have come from combining one's belief system with the laws of its government. john Locke stressed the importance of not allowing the State to combine religion and state law by explaining that man is entitled to authority over his individual conscience, and the State has no power to supersede that authority.
The question asks why a separation of church and state is inviolable or safe from violation.
In most nations of the world, the laws of a government are not based on a particular religion, nor is there an "official" religion.
Some countries, a few, have their laws based on a particular religion, with some "wiggle room" to not force a thief from having his hands cut off. This is not a facetious statement. Therefore the term inviolable does not describe all nations.
In the United States and in the majority of nations where officials in government are elected or appointed by elected officials, there is no "official State religion".
Since each of the non-official religion nations have different ways of stating this, perhaps one of the first nations, and the word "perhaps" should not be taken as being frivolous, can be seen in the First Amendment of the US Constitution of 1791. There has been some confusion regarding the the wording of this amendment and here is the wording, which covers a few other areas that a few nations don't live by:
Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.
In the United States, about 55 years ago, it was standard practice for a school teacher in a public school to read a verse from the "Old Testament" and have a class recite the "Lords Prayer". the two items covered Judaism and Christianity.
By doing so, it became clear according to the US Supreme Court, that this was "promoting a number of religions". So it was abandoned.
What has not been abandoned is Congress having a religious leader read a prayer before Congress begins. It has also not caused the word "God" to be removed from US currency and coins. No one really has presented a case that the Supreme Court has ruled in favor of to delete either practice.
US States and the Federal government still recognize religious holidays such as Christmas, as official days where schools and government are closed.
For the most part then, it can be said that US Federal, State, and local governments do not force a particular religion, nor forbid the practice of one, thereby not violating the 1st Amendment. ( oh, it's been general practice to have the US President and other officials to place a hand on the Bible and use the term, "so help me God".
Clearly creating a "State religion" would damage the rights of individuals, and allowing the free practice of a religion still holds.
This then is why the question is valid. The use of the term "separation of church and state" has come to mean that the first amendment cannot be violated.
It can be reasonable debated that the items mentioned where a Bible or a holiday of a certain religion is used or practiced is such a violation, but apparently the Supreme Court allows it.
The answer lies in the nature of the two entities. State is a secular institution whereas (the) church is a spiritual realm.
maryland i think
No, there is an official head of the church of england and it is not the queen or her representatives. When king henry 8th was alive, he created the church of england and down the road of history, the church and state separated.
it separated the church of the Eastern empire from the church of the Western Hemisphere.
To be separated from the Church of England.
Church of England
Virginia passed the Virginia Statute for Religious Freedom in 1786, five years before the Bill of Rights was created.
The Protestant church separated from the Catholic church during the Renaissance.
The Catholic Church was separated from government.
It is currently known as the Old Apostolic Church.
Virginia passed the Virginia Statute for Religious Freedom in 1786, five years before the Bill of Rights was created.
Pilgrims.
A compound that can be separated by electrolysis must be in the LIQUID state of matter.