When we learn the Torah, we work off the assumption that as the Torah is directly from Hashem, every word and even letter is there for a reason, and a lot of commentary and even Halacha is based on this.
When we learn Nach, do we also apply this principle and is it to the same degree? Neviim is written by other neviim, but they weren't as great as Moshe Rabbeinu, and Kesuvim weren't written by neviim at all.
The Zohar (Pinhas 213b) states that every letter of "Orayta" is necessary, it then explains why it states "שמרה" instead of "שמור" (T'hillim 86:2).
Similarly, the Malbim writes in his introduction to Yeshaya that every word of the Prophets are significant. As opposed to most famously the Rambam as was already answered.
The Pillars on which the Interpretation Rests, there are three.
a] Not found in the prophetic utterances a duplicate meaning in different words, not a duplicate meaning, not a duplicate statement, and not a duplicate expression, not two sentences with the same meaning, not two parables with the same allegory, and not even two double words.
b] Not found in the prophetic utterances and their statements, whether simple or double, words or actions placed by chance without a specific intention, until all the words, names, and actions from which the entire statement is composed, not only that they are compelled to come in that statement, but also the divine recommendation could not place another word beneath it. For all the words of the divine recommendation are weighed in the scales of wisdom and knowledge, arranged and preserved in a precise and counted measure of supreme wisdom, which alone will respond with its power to speak the truth.
c] Not found in the prophetic utterances a shell without content, a body without a soul, clothing without a wearer, an empty utterance devoid of lofty thought, a speech where intelligence will not dwell. For all these words of God are alive within them, a living spirit in their nostrils, a fearsome, mighty, and terrible spirit.
These three principles, the foundation upon which the interpretations of the prophets and the words in which the spirit of the Lord spoke in them and His word is on their tongues, will be acknowledged by every believer. For the spirit of the Lord spoke in the mouths of the prophets, and His word is on their tongues. Every believer with a whole heart, without a divided heart, will acknowledge that these are the words of the living God.
The Ramba'm in his Hakdama to Moreh Nevuchim says:
ודע כי משלי הנביאים יש בהם שני דרכים. מהם שכל מלה שבמשך ההוא יש בה עניין, ומהם מי שיהיה כל המשל מגיד לע כל העניין ההוא ויבאו במשך ההוא הנמשל דברים רבים מאד אין כל מלה מוספת ענין בענין ההוא אבל הם ליפות המשל וסדר הדברים בו או להפליג בהסתיר הענין הנמשל וימשכו הדברים כפי כל מה שראוי בגלויו של המשל ההוא. והבור זה מאד
Know that the figures employed by prophets are of two kinds: first, where every word which occurs in the simile represents a certain idea; and secondly, where the simile, as a whole, represents a general idea, but has a great many points which have no reference whatever to that idea: they are simply required to give to the simile its proper form and order, or better to conceal the idea: the simile is therefore continued as far as necessary, according to its literal sense. Consider this well.
The Ramba'm goes on to bring as an example of the first type, where every word is needed as part of the nevua, Ya'akov's dream of the ladder. And as an example of the second type, the Ramba'm brings a long mashal from mishlei (7:6-26), which compares indulgence to adultery. So the Ramba'm says that some words are not there to be learned from, only to beautify the parable. However, this seems to only apply to parables.
Even this is contested, as the Shem Tov on the Moreh Nevuchim says:
תמצא רוב המפרשים בהרבה מקומות יספקו על הרב ולא ידעו ולא יבינו בחשכה יתהלכו
...You will find the majority of mefarshim in many places doubt the [Ramba'm], and "they do not know and have not understood, and walk in the dark"
Note: I'm still looking for those "majority of mefarshim" that argue with the Ramba'm, I haven't yet found someone who does so outright. It's also possible the Ramba'm applies this to the Torah as well as Na'Ch, which would mean this isn't as good an answer, because the question was asked assuming we learn something from every word in Torah.
Yes. All of the written Torah, including nach, are very precise, even the poetic texts in most of kesuvim. Although we may not know all of the details (on the contrary, it is impossible to begin to grasp the true depth of a single verse) there a plethora of reasons behind everything, on all the levels of pardes (pshat-simple meaning, remez-elucidations, drush-exegesis, and sod-the secrets [kabbalah etc]) and on a chassidic level etc.
I saw in the Alshich's commentary on Shir HaShirim's first pasuk this Yom Tov something that might suggest an answer to your question. What do you supposes about it?
או יאמר בשום לב אל מאמרי רז"ל יש יאמר כי שיר השירים על הים נאמר מפי מלאכי השרת וי"א בסיני מפיו ית' וי"א באוהל מועד והנה לעומ' הסכמ' רז"ל ע"פ המקרה כי שרת' על שלמה רוח הקודש ואמר שלשה ספרים שיר השירים ומשלי וקהלת ואם אמרנו שנשכחו והחזירו ברוח הקודש איך יאמר אשר לשלמה והלא עתניאל בן קנז החזיר כמה הלכו' שנשתכחו מישראל בפלפולו ולא נקראו על שמו ולמה יגרע על היות מכח פלפול אך לזה נשית לב אל אומר' אשר לשלמה ולא אמר שיר השירים לשלמה כד"א שיר המעלות לשלמה אמנם הוא כענין מאמרנו בביאור ספר משלי על תאמרו יתברך בימי מרע"ה אליעזר בני או' עגלה בת שנתה כו' והלא כמו זר נחשב יחשוב מאמרו ותורתו בשם איש האדמה ולא עוד כ"א כמה דורות טרם הולדו אך הוא כמדובר שם כי כל נפש ונפש מישראל יש לה חלק בתורה מתייחס אל בחינתה וזה חסדו אשר יעשה הוא יתב' עם כל איש ואיש לבלתי חדש בעולם שום דבר מהמתייחס אל בחינת נפשו רק מפיו בכל דור ודור ולא עוד כ"א גם הוא ית' עצמו ולא יזכיר מאמר הקדו' ההוא רק בשם בעליו כי מאז טרם יולד יאמר זה חלק פלוני כן הדבר הזה גם שהוא יתברך או מלאכיו אז שררו השיר הזה מאז בהחיל' הם אמרו שיר השירים אשר לשלמה לו' זה שיר מהשירים אשר לשלמה כלו' אשר לו חלק נפשו מעין שבח מאמרו יתברך אליעזר בני אומר פרה בת שתים כו' כי מאז גלה כי הדין הוא לאליעזר בנו הוא חלק נפשו כן אמר שיר השירים אשר הוא לשלמה שלו חלק נפשו ומעותד ליאמר על פיו בהתחדש בעולם ומעתה נאמר אשר הוא לו:
Relevant to our discussion is what Chazal say (Shir HaShirim Rabba 1:1:12): "There are those who say that Shir HaShirim was said by the splitting of the sea, and those who say that Hashem said it at Har Sinai, and those who say He said it in the Ohel Moed". This contradicts the previous Midrash (ibid 1:1:10), where Chazal state that Ruach Hakodesh rested on Shlomo and he said 3 sefarim: Shir HaShirim, Mishlei and Kohelet. If you say that they once knew it and it was forgotten, and he remembered it with Ruach Hakodesh, how can it be attributed to Shlomo? Antiel Ben Kanaz brought back many [forgotten] halachot through incredible pilpullim and they are not attributed to him! Note that the phrase is "אשר לשלמה", it doesn't say "שיר השירים לשלמה", like we say "שיר המעלות לשלמה". It's like I wrote in my commentary on Mishlei (22:17), I explain a Midrash where Hashem is quoted saying "Eliezer my son states that the calf must be a year old...". Isn't that strange? Hashem is expounding His own Torah, basing His own words on the way some mortal will understand them born several generations in the future! As we explained there, in Hashem's kindness, each Jewish soul has a portion in the Torah to which he can relate, and in that area he can make a chiddush to the world, and in each generation chiddushim are conceived by Torah scholars who are able to understand them in a way that was not previously understood and Hashem Himself will not state those chiddushim without mentioning the name of the one who will introduce it to the world, as we see in this case of Rabbi Eliezer where Hashem quoted this halacha in his name way before his time. Similarly, Hashem or the ministering angels may have sung Shir HaShirim many generations before Shlomo, yet still it begins with "שיר השירים אשר לשלמה", i.e. "Shir HaShirim which was apportioned to the soul of Shlomo". In the case of R' Eliezer, the halacha was already in his soul at Sinai, and similarly with Shir HaShirim, it belonged to Shlomo's soul even before he lived and hence it is attributed to him and given his name.
We can see from this that even something from Ketuvim was already in existence, said word for word by Hashem Himself (or a ministering angel), at or around Sinai times. This goes with what I've learned in shiurim all my learning life: all of Tanach is "word perfect", i.e. the premise your are asking about in your question.
It goes further, and states that halacha itself works like this. Perhaps we can say the Talmud is word perfect too. Your own chiddushim were in your soul back at Sinai.
How great is Torah, Yisrael and Hashem.
The famous teaching of
וּכְשֶׁבָּרָא הַקָּדוֹשׁ בָּרוּךְ הוּא אֶת עוֹלָמוֹ נִתְיָעֵץ בַּתּוֹרָה
When Hashem created His world, He consulted the Torah
is a core teaching in Torah. It is so foundational and primary that it is the very first teaching in both Midrash Rabbah and Midrash Tanchuma. The Midrash Tanchuma declares the point that every word and letter is perfect and purposeful:
מַהוּ קְוֻצּוֹתָיו תַּלְתַּלִּים? עַל כָּל קוֹץ וָקוֹץ. תִּלֵּי תִלִּים שֶׁל הֲלָכוֹת
What is meant by "His locks are curled" [Shir Hashirim 5:11]? It means that each crowned stroke on the letters of the Torah contains heaps and heaps of law. (Midrash Tanhuma-Yelammedenu, trans. Samuel A. Berman)
This is the source for the concept.
It then proceeds to give numerous examples of how if a single letter were changed, the world (which was created from the Torah) would be destroyed. Notably, it brings examples from Torah, Neviim and Ketuvim:
It is written in the Torah: Profane not My Holy Name (Lev. 22:2); but if you should change the chet in the word yechallelu (“profane”) into a heh, the word would read “praise,” and you would thereby destroy the world.
"They have lied against the Lord" (Jer. 5:12), if you should change the preposition bet (“against”) into the preposition kaf (“like”), you would thereby destroy the world.
"Let everything that hath breath praise the Lord" (Ps. 150:6), if you should alter the heh in the word tehallel (“praise”) into a het, the word would read “profane,” and you would thereby destroy the world.
The Midrash finishes the point by saying:
וְאִם אוֹת אַחַת כָּךְ, כָּל שֶׁכֵּן הַתֵּבָה כֻלָּהּ, לְכָךְ נֶאֱמַר: קְוֻצּוֹתָיו תַּלְתַּלִּים
If a slight change in a single letter can produce such drastic consequences, how much more so the alteration of a complete word.
and then proceeds to demonstrate how the world is constructed according to the blueprints of the Torah, and notably gives examples from Neviim and Ketuvim:
It [the world] was with the assistance of the Torah that God stretched out the heavens and established the earth, as it is said: "If My covenant be not with day and night, if I have not appointed the ordinances of heaven and earth" (Jer. 33:25). With it, He bound up the sea lest it should go forth and overflow the world, as it is said: "Fear ye not Me? saith the Lord; nor will ye not tremble at My presence who have placed the sand for the bound of the sea" (ibid. 5:22). With it, also, He locked up the deep so that it might not inundate the world, as is written: "When He set a circle on the face of the deep" (Prov. 8:27). Similarly, He fashioned with it the sun and the moon, as is said: "The Lord giveth the sun to light the day, the ordinances of the moon and the stars to light the night. Who stirreth up the sea, that the waves thereof roar, the Lord of hosts is His name" (Jer. 31:35). Hence, you learn that the world was founded upon the Torah.
