King Charles will be crowned a week from today in Westminster Abbey, a religious site with a direct connection to royalty since Edward the Confessor built the predecessor to the current building put up by Henry III, and which became a "royal peculiar" by Elizabeth I. His right to be monarch will be acclaimed by the peerage and ordained by the Church of England speaking on behalf of God.
The King will in turn make a covenant with his people by uttering the coronation oath. The following extract is from the oath sworn by his mother in 1953, as administered by the Archbishop of Canterbury, and I assume he will use the same wording.
Will you to the utmost of your power maintain the Laws of God and the true profession of the Gospel? Will you to the utmost of your power maintain in the United Kingdom the Protestant Reformed Religion established by law? Will you maintain and preserve inviolably the settlement of the Church of England, and the doctrine, worship, discipline, and government thereof, as by law established in England? And will you preserve unto the Bishops and Clergy of England, and to the Churches there committed to their charge, all such rights and privileges, as by law do or shall appertain to them or any of them?
The other parts of the oath relate to everyone who is a subject of the King, but this section refers only to the Protestant religion. It is worth considering what this means. According to the Office for National Statistics, the results of the 2021 census show:
For the first time in a census of England and Wales, less than half of the population (46.2%, 27.5 million people) described themselves as “Christian”, a 13.1 percentage point decrease from 59.3% (33.3 million) in 2011; despite this decrease, “Christian” remained the most common response to the religion question.
“No religion” was the second most common response, increasing by 12.0 percentage points to 37.2% (22.2 million) from 25.2% (14.1 million) in 2011.
Less than half of the population is Christian but within that number are Catholics, Baptists, Methodists, Quakers, members of the various Reformed churches and so on. The Church of England represents only part of a minority, but it is this unrepresentative group that the King will swear to defend, to protect its privileges and to to the utmost of his power, maintain its doctrine and worship. And by declaring his oath in the most sacred place that he acknowledges, he is swearing that the Protestant religion is true and by implication all other versions of Christianity, never mind the beliefs of the rest of the country, are not.
Charles may the first monarch in British history to be in this strange position, apart from Edward VI and Elizabeth I who implemented the Protestant takeover of the church after they were crowned. Unlike them, he cannot say "I am the king, everyone believe what I believe or I shall persecute you, even unto death". He will take his oath to represent some of his subjects and, unless the wording of the oath is to change drastically, will omit the rest of us.
During the rest of his lifetime, and that of William his heir, it is likely that Christianity will continue to decline and that the majority of Britons will describe themselves as of no religion. Will there come a time when it is no longer reasonable for the King to defend the privileges of a small minority on the grounds that that is what God wants? God remains silent on the subject.