Under divine monarchy (the Byzantine model) the monarch believes himself subject to God, and the people believe themselves subject to God - hence to the monarch (if he be a genuine monarch, properly devout).
All authority comes down from God and via the monarch. And that authority is divine.
Under modern democracy, authority comes from man - but not from a particular man, but from a mass of men - from the system used to determine the will of a mass of men.
At one level authority, therefore, comes from force, from the decision of the biggest group.
But not really.
Perhaps, then, the most powerful group?
But the group - in a modern democracy - is itself merely a kind of contingent mathematical average of a large number of individual opinions.
There is no group mind.
The democratic view is atomic - there is a democratic view (which derives from a particular system of discovering the democratic view) and it applies only to a specific 'issue' - or even more precisely to the way in which a particular issue is framed: the choices offered: the question to which is asked 'yes or no'.
Is there a mystical authority of democracy possible? Yes, probably, in a devout society of people each of who is praying for divine guidance, and whose deliberations are informed by such prayers.
The early 'ecumenical councils' of the Christian Church would be of this type, and probably the town meetings of early New England would be another instance.
Probably - at a lower level - the college meetings of the Fellows of an Oxford or Cambridge college up to the early 19th century - in so far as most of them have internalized the spiritual values of the college, and most of the fellows individually and sincerely wished to maintain these values.
(Of course many such colleges became corrupted by individual careerism and idleness. I am talking of those which did not.)
However, I believe that for such a system of democracy to be maintained also requires a sincere and cohesive religious underpinning - once this was removed from college governance, a process of change began which was first and briefly meritocratic (short term benefit) but soon and irreversibly degenerative (long term harm).
(And it is noteworthy that the original method of college governance was autocratic: the Master/ Warden/ Principal dictated policy and the Fellows/ Regents were merely temporary, fixed-contract employees.)
But to articulate a vision of democratic authority is to recognize its utter and complete lack in modern societies.
We 'believe' in democracy as the crudest form of magic: somehow democratic voting processes have the (literally) incredible property that they will (although themselves lacking any specific rationale or validity, and being widely varied, and prone to manipulation and cheating) magically lead not just to good choices and policies, but will (somehow) transmute the base metal of individual, short-term selfishness into wise, long-term public spiritedness.
Do we actually believe this?
No. Which is why there is no authority.
But - lacking any allowed alternative - we are not allowed to deny it.
Which is why the situation is desparate and irremediable.