Are there unnecessary words in torah?

I've been taught, often enough that I thought it was universal, that there are no unnecessary words in torah (chumash) — every word is there to teach us something. I've seen plenty of discussions in the g'mara that seem to follow this principle, too, understanding that two similar-seeming verses (or words) are there to teach two different principles because they can't be serving the same purpose.

For example, Sanhedrin 64b (summarized in point 3 of this outline, h/t @ba) asks why the torah says three times that one is chayav karet for idolatry and then finds three interpretations. It doesn't say explicitly there that each of the torah's three statements must be "consumed" by a different halacha, but this lesson from the Virtual Beit Midrash (Yeshivat Har Etzion) states the rule explicitly but without citation in a discussion of Kiddushin 72b, discussing a baraita:

The gemara begins its analysis of the beraita by questioning the reasoning behind Rabbi Yossi's position. The gemara explains that, in the context of those who are genealogically unfit to marry into the broad Jewish community, the Torah (Devarim 23:3-9) employs the term "congregation" (for example, a mamzer may not "enter the congregation of God") five times. Since the Torah could have simply listed all the different categories (mamzerim and converts of Amonite, Moabite or Egyptian descent) and stated once that they may not enter the congregation, the gemara assumes that the word "congregation" must have been used extra times in order to teach further details about these prohibitions. This is quite characteristic of Talmudic methodology. Since there are no unnecessary words in the Torah, words that appear extra must be there in order to teach some detail that we would not have known otherwise.

I have also heard, but don't know where, that a perfect torah would not need to include superfluous words (along the idea of @WAF's comment below), and of course God's torah is perfect. I'm not sure how much weight to give a human interpretation of divine intent.

Today I read that this "rule" about unnecessary words is not universally held.

What sources are there for each position? Who holds that there are no unnecessary words, and who does not, and on what basis?

Answer

The Ramban writes in his hassagos to shoresh sheni of the Rambam in sefer Hamitzvos that there is not even one extra letter in the Torah:

אבל הכתוב יכלול הכל כי אין הפשט כדברי חסרי דעת הלשון ולא כדעת הצדוקים. כי ספר תורת ה' תמימה אין בה אות יתר וחסר כולם בחכמה נכתבו

Rather, the verses contain all [of the ideas contained in the d'rshos of Chazal] for the explanation of the text is not [meager] in accordance with the words of those lacking intelligence, nor like the opinion of the Sadducees. For the Torah scroll of God is perfect, it has neither a superfluous nor a missing letter, they were all written with wisdom. (Trans. my own).

This is clearly stated by Rabbenu Bachye as well in his commentary to Genesis (47: 28):

אבל התורה כולה רמזים, אין בה תיבה ואות שלא נאמר לענין הכרחי ומוצרך

"The Torah is all hints; it has no word or letter that was not stated for necessary reason" (Trans. my own).

Also noteworthy is the comment of Rabbenu Avrahan ben HaRambam in his commentary to Exodus (20:20) where he seems to state this as well:

אין כפל במקרא

There is no repetition/superfluity in the Torah.

see below regarding his intent here

This is a common theme among the commentaries of the Acharonim. An example of this is R. Yaakov Emden's commentary to Ashrei where he writes as follows:

It is true that those who interpret Scripture literally are incapable of explaining the nature and the reason for the repetition of meliẓah in Scripture in so many different forms. Verily, the initiated will understand … that it is not without significance and it is not by chance that there is a multitude of synonyms for the same matter and changes in language and terminology (meliẓah). (Translated by R. Dr. J.J. Shachter’s Jacob Emden: Life and Major Works p. 282.)

For similar statements by Malbim, and a discussion of their historical context, see: https://judaism.stackexchange.com/a/71508/8775

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Rabbenu Avraham is approving of R. Saadya Gaon's distinction between לא תעשון אתי אלהי כסף and the end of the verse ואלהי זהב לא תעשו לכם. Regarding which he says אין כפל במקרא.

Rabbi Ezra Labaton z"l (in his dissertation here p. 154) understands these words to be Rabbenu Avraham's conclusion (that is an independent clause about the nature of Torah.) Accordingly, this would be similar to the Ramban.

However, it is not clear to me that Rabbi Labaton's reading is correct, for the whole line of Rabbenu Avraham reads:

ומאמרו אחרי כן 'לא תעשו לכם' אזהרה על קבלת הצורות והתמונות ולפי זה אין כפל במקרא

In context it seems likely that he is merely saying that Rav Sadya Gaon's explanation has the benefit of avoiding superfluity, which is avoided according to his explanation, not that scripture is never superfluous.