@Stralvan
Segments of Christianity have taken the position that the official interpretation of doctrine comes from within the ordained clergy; that Catholicism had taken it to the point to forbid translations of the scriptures into the common tongues to insure that interpretation only came from the hierarchy of the church was part of what led to the Reformation.
Various segments of Judaism have also taken this stance at various times. As has Islam.
Other religious traditions have also had it that the interpretation of signs, portents, and messages from the relevant deity were the purview of the priesthood within that faith.
It does happen in this world. It is not only something that happens in works of fiction.
Look at the history of Europe; the stance of the established faith influenced a great many things, and at times the church hierarchy was filled with very unscrupulous individuals who used their position for the aggrandizement of their secular relatives, or their home nation, etc.
It has the potential to become a problem anytime secular policy is required to be in line with religious doctrine, as when this occurs those in the position of interpreting for the deity suddenly gain great temporal power, and, inevitably, some prove unworthy of this responsibility.
Even those worthy of the responsibility, in that they don't abuse it deliberately for the benefit of those they care about, still have the potential to be in error in their interpretations.
One sees it with Islam, in those countries where the religious leadership gains temporal power.
It's happened with Christianity since the early years.
Judaism has had problems with this.
And it doesn't take all that much research to determine that it's been a problem with a great many faiths which developed outside the Middle East.
Any faith which has established doctrine, someone was involved in determining what that doctrine is.
Someone, at a minimum, said, "These writings constitute the Holy Works; all others are in error at some level."
What they selected as being the Holy Writings were those which fell in line with their personal interpretation of the will of their deity.
So long as there is free will, there's the potential for misinterpreting, knowingly or unknowingly, any messages from the deity.
None of this gets into the question of whether the deity has your best interest at heart.
Any deity that actually interacts with their creation has an agenda.
The very act of creation says that there is an agenda, something that made expounding the effort of worth to the deity.
I will admit, I'm most familiar with what has occured within Christianity in Europe and North America. Both from looking at it from the outside, when studying European and New World history, and from within, in that at various times I was an evangelical charismatic, a member of several semi-mainstream Protestant denominations, and LDS. In addition, for a period I was Bahai, and my upbringing was as a Unitarian Universalist.
I've been very fortunate, in that all the religious leadership I had direct contact were good people, sincere in their faith and very well intentioned. However, none of them had temporal authority derived from their religious status.
I keep waffling back and forth in my reaction to how often a corrupt clergy or evil god appears in Isekai; it depends upon how cynical I'm feeling at the time.
All that aside, I too think this manga is worth continuing to read.