This is important, not least because the medieval chroniclers are renowned for their inaccuracy when it comes to figures. Medieval writings describe deaths of tens of thousands in cities that could not possibly have had these populations. (Similar problems exist in the descriptions of contemporary battles - sizes of armies and casualties routinely don't match reality).
Zieglar settles on a figure that says that approximately a third of Europe's population died. The plague didn't have equal impacts - the rich suffered proportionately less, though no one was spared. Occasionally, in an attempt to find blame, frightened populations massacred those they thought had incurred God's wrath - the Jewish pogroms of the time are well documented and often seemed to have, at least the tacit support of the local establishment.
There were other interesting by-products of the plague, and the inability of the medieval mind to come to terms with what was happening - the Flagellant movement of religious people, who travelled from towns to cities on the continent, whipping themselves in front of crowds being one of these.
But the Black Death did shake the medieval world. It helped change the way many viewed the world. As Ziegler says:
The Black Death did not cause the Reformation, it did not stimulate doubts about the doctrine of the Transubstantiation; but did it not cause a state of mind in which doctrines were more easily doubted and in which the Reformation was much more immediately possible?Because the Black Death had not spared anyone, because the church had been proved ineffectual, some of the most important pillars of society were undermined. As Ziegler concludes, the world was never quite the same again.