Hebrew has never been extinct. There have been documents in Hebrew continuously for a very long time (though the script has changed over time), and it has been used in spoken prayer for just about as long. Even at times when writing in the Hebrew language was less common, a) it was still being read, such as during Torah readings and b) the letters were still being written, but used as part of a Judaized version of the native language- the most famous example in the contemporary world is Yiddish, which is a language spun off of a German dialect which is written in Hebrew characters. But there are many others, including Judeo-Arabic (in which Maimonides wrote the majority of his works, for example), Judeo-Spanish (also called Ladino), and Judeo-Italian.
Even besides for these written languages which used Hebrew characters, religious works- and there were MANY of these- continued to be written in Hebrew for hundreds of years. In fact, books began to be printed in Hebrew not long after the invention of Gutenberg's printing press, and the Jewish printing industry was a very prolific one. (One of the coolest things I have ever seen is a copy of a Hebrew religious work called the Arba'ah Turim which was printed with movable type from Spain, paper from Italy and on a press in the Ottoman Empire, reflecting the forced migration of the printer from Spain after the expulsion in 1492.)
Remember also that for many hundreds of years, Hebrew was considered an important language to many Christians. Especially after the Protestant Reformation, there were many Hebraist Christians (who often had personally negative feelings toward the Jews- these included Johannes Buxtorf the Elder). This continued all the way through at least the 18th century, when colleges like Harvard and Yale had Hebrew as a required classical language.
Hebrew continued to be used in the 19th century, though it returned to being the province of Jews by and large, and specifically religious Jews. For all of those hundreds of years, any decently educated (male) Jew could read and understand at least a little bit of Hebrew, often much more, and any decently educated (female) Jew and the less educated male Jews could at least read and understand Yiddish, which meant knowing Hebrew characters. However, in Lithuania in the mid-19th century, the Eastern European Jewish Enlightenment (which came about 100 years after its German Jewish counterpart) caused a small resurgence in the idea of writing in Hebrew, with non-religious poets like YL Gordon writing long epic poems in Hebrew, often skewering religiosity.
Now let's talk about the Holy Land/Israel/Palestine/whatever you want to call it at whatever time. Jews had been going there in drips and drabs for hundreds of years. Biggish groups started coming in the early 1800s from Europe, called the Old Yishuv, and they spoke in Yiddish. Other groups came from Yemen, and they spoke in Arabic. No Hebrew yet as a spoken language.
Then came Eliezer Ben-Yehuda. When he came to Jerusalem in the 1880s as part of the highly ideological First Aliyah (rising up), he became intensely focused on rebuilding Hebrew as a SPOKEN language, to unify all of these disparate people who spoke all these different languages- Yiddish, German, Arabic, French, Polish, Russian, etc. He had a huge base to work off of- as mentioned, Hebrew was maintained as a written language for thousands of years, and it was read aloud both in its own form and as part of these Judeo-languages. His role was mostly to create a systematic spoken language- with many words which needed to be invented as they weren't really used in religious writings (not all of these ended up being used- for example, his original word for "train" was a Hebrew phrase that means "chariots of fire and iron," which I honestly think should totally have been the one everyone ended up going with) and creating a systematic lexicon. He helped establish what became the Academy of Hebrew Language, which still exists today, and is the reason why Hebrew went from being an academic language to a spoken one with films, literature, slang, and more.
Think of Hebrew less as a revivified dead language and more as if someone had decided to translate Harry Potter (the books and the films) into the Latin of the Catholic Church. You would need to add a lot of colloquial usage, as well as create a community of people who speak and read this new colloquial Latin well enough to appreciate having Harry Potter in that language.

EDITED: I forgot to talk about the changes in pronunciation of Hebrew over time, and part of the reason is that I'm not super well versed in that. But suffice it to say that, understandably for a language which has been in use for an extremely long time in whatever form, pronunciation has not stayed static. One of the things about modern Hebrew is that it codified the pronunciations of certain letters- for example, there are six Hebrew letters which can be written with or without a dagesh, or dot inside the letter,and only three of these have practical differences in modern Hebrew. The other three have practical differences which have either fallen out of public memory or are considered somewhat archaic/old-fashioned/localized to a particular region. There are a lot of different scholarly arguments about which local variant of Hebrew (from before the standardization of modern Hebrew) is "most authentic." There have also been changes in grammar, from Biblical grammar to modern grammar, and that is way out of my wheelhouse. I may see if I can get a friend of mine to write up a bit about that.
Also, I just Googled and apparently someone DID translate Harry Potter into Latin... I am so intrigued by that.