Do Jews accept The Book of the Wars of the Lord (סֵפֶר מִלְחֲמֹת יהוה) as an authentic part of Tanach

Question

Do Jews accept The Book of the Wars of the Lord (סֵפֶר מִלְחֲמֹת יהוה) as an authentic part of Tanach?

"From there they set out and camped on the other side of the Arnon, which is in the desert and bounding the Amorite territory. For Arnon is the border of Moab, between Moab and the Amorites. That is why the Book of the Wars of the LORD says: '... Waheb in Suphah and the ravines of Arnon, and at the stream of the ravines that lead to the dwelling of Ar, which lies along the border of Moab.'" Numbers 21:14-15

https://en.m.wikipedia.org/wiki/Book_of_the_Wars_of_the_Lord

Answer 1

Nachmanides writes:

ודרך הפשט ב"ספר מלחמות ה'", שהיו בדורות ההם אנשים חכמים כותבים ספר המלחמות הגדולות, כי כן בכל הדורות, ובעלי הספרים היו נקראים מושלים, שנושאים בהם משלים ומליצות, והניצחונות הנפלאים בעיניהם מיחסים המלחמות ההם לה', כי לו המה באמת.

And in the simple meaning of the "Book of Wars of G-d": In those generations, there were wise men who wrote about the great wars, as it is in all generations. And the authors of the books were called "Moshlim (parable makers)" as they would bear parables and lessons (ie. the lessons that are derived from the parables). And the triumphs that were wondrous in their eyes, they would attribute to G-d, because they were truly His.

I understand Nachmanides as saying that this type of book was a common thing for people of the time to write books about. And Jews wrote these types of books too. In fact, if you want more information about this war, you could check out the book that Jewish writers kept about the wars they fought.

So at least according to this explanation, I don't think it was meant to be a book of Tanach as much as a diary of national wars.

Answer 2

According to the Midrash Aggadah it is indeed an authentic part of Tanach; it is in fact the second book of Tanach, the Book of Exodus:

זה ספר ואלה שמות שבו כתוב המלחמה שעשה הקב״ה עם מצרים והמלחמה שעל הים

This is the book of V'eileh Shemot (Exodus), in which is written the war that God waged with Egypt, and the war by the sea.

Note, though, that many commentators understand it to be a separate book, including:

• Ibn Ezra
• Bechor Shor
• Chizkuni
• Ramban
• R. Bahye b. Asher (citing Ibn Ezra)
• R. Jacob b. Asher (citing Ramban)
• Ibn Kaspi
• Ralbag
• R. Samson Raphael Hirsch

There are also some commentators (Rashi, Rashbam, Shadal, et al.) who interpret it as being not a book at all, but a telling of events.