@infinitywithoutparallel oh hang on - I misunderstood your comment. My bad!
You’re asking whether we can accurately read ancient Hebrew, because the Hebrew language died and was reconstructed, and so, can we REALLY read ancient texts in Hebrew accurately if our modern Hebrew is a reconstruction. Which is a good and interesting question.
So, Hebrew is a language, and languages evolve over time. As a speaker of modern day English, you wouldn’t be able to read Chauscer in Middle English, and you wouldn’t be able to read Beowulf in Old English. It’s changed too much, because of all the invasions (viking invasions, norman invasion, etc) and because of the influence of Latin as the language of science. However, Hebrew did NOT change that much, in part BECAUSE it “died.”
When we say a language is dead, that doesn’t mean no one can speak, read, or write that language. It means no new words are being added to it, and it has no more native speakers for whom it is their first language. We actually can fluently speak and write many “dead” languages today, most notably Latin, with total accuracy. Hebrew stopped being spoken by everyday people, but it was maintained as a language people had to learn because Jews have always kept the Tanakh in Hebrew and prayed in Hebrew. A language “dying” doesn’t make it lost, it’s more like it crystallizing. Dead languages preserve BETTER because they aren’t changing constantly.
When Hebrew was revived as a living language, it DID undergo some small changes.
We now use SVO sentence order, not the classical SOV. So, what used to be “I to the store went” in classical Hebrew, we would now just say “I went to the store.”
A lot of words got added to the language to describe the things that now existed in the world but not in the Hebrew language, like computer. These mostly have roots in the Hebrew language - we call a computer a machshev, a “thinker,” from the root word for to think. Some though, are loan words, like balagan, which comes from Russian and means “a big mess.”
We less often use pronoun endings, because we now have a word that implies possession. So instead of saying “chatuli” for “my cat” we would more likely say “chatul sheli.” Not always though! Pronoun endings are still perfectly valid grammar.
We use a different construction for possessives. Classical Hebrew uses a construction like this: “chatul Matan” would mean “Matan’s cat.” However, we now have a word for “of” so we would more commonly say “chatul shel Matan.” However, again, both are valid and still used. And the word for of, shel, isn’t as old as the Torah, but it does start to appear in the later books written in the Tanakh.
There used to be two forms of the word “I,” ani and anochi. Now we mostly only say “ani.” Same for “we,” which used to be both anu and anachnu, and now we mostly only say “anachnu.”
Those are pretty much all the differences in grammar. As you can imagine, it’s very easy for modern Hebrews speakers to read older writings with those more formal grammar styles! Easier than for us to read Shakespeare, actually.
There’s a few other considerations though.
Hebrew is now written using a script called ketav ashurit, which developed during the exile in Babylon. Before that, a more angular style called ketav Ivrit was used (and is still used by Samaritans). We have other scripts too, like cursive and Rashi script. However, unlike the development of different scripts for English, each letter directly corresponds to an ancient one exactly. Think of them as different fonts. Most Jews don’t read ketav Ivrit today, but many can, and it’s not hard to learn.
The spellings of some words changed VERY slightly from the ancient to the modern day. Mostly, we added extra ו and י letters to some words, to represent o and i sounds that were already there. Again, unlike English, where spelling was a free for all, these are VERY slight changes, and it’s easy to read them either way.
We aren’t EXACTLY sure about the pronunciation of ANCIENT Hebrew. However, by comparing multiple surviving accents and dialects of Hebrew with what we know about other semetic languages like Amharic, Aramaic, and Arabic, we can make very educated guesses. None of this would effect meaning at all! Just the way it sounds.
There are a FEW very specific nouns in the Torah that we aren’t exactly sure what they mean, because even by the Septuagint was translated people had stopped using those words. We can usually tell from context what kind of word they are - for example, we can’t be exactly sure what birds are being listed as unkosher, or what stones were in the High Priest’s breastplate. But we have very educated guesses from context, preserved in the Talmud.
So, TL;DR - Hebrew HAS changed some over the years, but actually comparatively very slightly. A modern Hebrew speaker can read and understand ancient Hebrew with no difficulty. It is the same language, with less differences between Ancient and Modern Hebrew over a span of 5,000 years, than between sixteen and twenty-first century English, a mere 500.