I just heard one of our parish priests say that the Latin used as well as the Greek was not the vernacular of those languages.
Correct, it would have been the “academic” version of those languages.
The latin of Cicero was not spoken by the people of Rome at the time, nor even by Cicero, unless engaged in rhetoric.
In the US today, you can find many dialects that are different than what you hear in our courts, on the newsy and in academic paper or university classrooms–spoken by the same people who ain’t gonna talk like that formally . . .
The academic version is a useful base/centralization, and can generally be understood by the others.
In a not-so-completely-unrelated note, I’m wondering how long Americans will understand international English. Today, the international tongue is mid- to late- twentieth century US English (much to the dismay and anger of the British

). I expect that to remain frozen, much like Latin and French did for their international purposes, while the spoken US dialects will continue to change (perhaps more slowly than in the past due to broadcast media).
And
Norman French is still used at British coronations and maybe a couple of other ceremonial events. The people who can speak it can be counted on one hand, and their purpose is to tutor the monarch through these bits that noone can understand anyway . . .
hawk