Considering that religion from the relevant eras was largely a mechanism of control (or, less ominously, societal orchestration), this is not surprising.

I'd very much like to read an exploration of the relationship between the rise of irreligious social constructs and the decline of the importance of religion in modern states.

You don't need to go any further that "Render to Caesar the things that are Caesar's; and to God the things that are God's." to see the principle of separation of church and state laid in a religious text.

Not that it was ever followed in practice in the centuries that followed.

If I'm not mistaken this is found only in the book by the apostole who was a tax collector for Caesar. :-)

That was sort of the whole point of the parable.

...still canon.