Who's Zachariah??

There is a book in the Bible titled 'Zachariah' after a prophet of the two tribe kingdom of Judah
The book is the eleventh of twelve books called the Minor Prophets.

"Z" for Zachariah as it is the last letter of the alphabet implies the last of something.
"A" for Adam, who was the first man, "Z" would mean the last man. I think.

Its a reference to the last living man.
Adam started human civilization and Zachariah finishes it.

In the book I believe that Ann talks about this.
Where she had an alphabet book when she was a child that named characters from the bible in each letter "A is for Adam." Etc and ending with "Z for Zachariah"
And when Ann was a child she though since Adam was the first man on earth and was the first person in the book then if Zachariah was the last person in the book he must be the last man on earth.

And that thought mirrors the events in story since the characters believe they're the last people on earth.