Of "the book of the wars of the Lord" nothing is known except what may be gathered from the passage before us. It was apparently a collection of sacred odes commemorative of that triumphant progress of God's people which this chapter records. From it is taken the ensuing fragment of ancient poetry relating to the passage of the Arnon River, and probably also the Song of the Well, and the Ode on the Conquest of the Kingdom of Sihon Numbers 21:17-18, Numbers 21:27-30.
What he did - The words which follow to the end of the next verse are a reference rather than a quotation. Contemporaries who had "the Book" at hand, could supply the context. We can only conjecture the sense of the words; which in the original are grammatically incomplete. The marg. is adopted by many, and suggests a better sense: supplying some such verb as "conquered," the words would run "He" (i. e. the Lord) "conquered Vaheb in Suphah, and the brooks, etc." Suphah would thus be the name of a district remarkable for its reeds and water-flags in which Vaheb was situated.

The book of the wars of the Lord - There are endless conjectures about this book, both among ancients and moderns. Dr. Lightfoot's opinion is the most simple, and to me bears the greatest appearance of being the true one. "This book seems to have been some book of remembrances and directions, written by Moses for Joshua's private instruction for the management of the wars after him. See Exodus 17:14-16. It may be that this was the same book which is called the book of Jasher, i. e., the book of the upright, or a directory for Joshua, from Moses, what to do and what to expect in his wars; and in this book it seems as if Moses directed the setting up of archery, see 2-Samuel 1:18, and warrants Joshua to command the sun, and expect its obedience, Joshua 10:13."
What he did in the Red Sea, and in the brooks of Arnon - This clause is impenetrably obscure. All the versions, all the translators, and all the commentators, have been puzzled with it. Scarcely any two agree. The original is את והב בסופה eth vaheb besuphah, which our translators render, what he did in the Red Sea, following here the Chaldee Targum; but not satisfied with this version, they have put the most difficult words in English letters in the margin, Vaheb in Suphah. Calmet's conjecture here is ingenious, and is adopted by Houbigant; instead of והב vaheb, he reads זרד zared. Now a ז zain may be easily mistaken for a ו vau, and vice versa; and a ה he for a ר, resh, if the left limb happened to be a little obliterated, which frequently occurs, not only in MSS., but in printed books; the ב beth also might be mistaken for a ד daleth, if the ruled line on which it stood happened in that place to be a little thicker or blacker than usual. Thus then והב vaheb might be easily formed out of זרד zared, mentioned Numbers 21:12; the whole might then be read, They encamped at the brook Zared, and they came to Suphah, and thence to the brook Arnon. Take the passage as we may, it is evidently defective. As I judge the whole clause to have been a common proverb in those days, and Vaheb to be a proper name, I therefore propose the following translation, which I believe to be the best: From Vaheb unto Suph, and unto the streams of Arnon. If we allow it to have been a proverbial expression, used to point out extensive distance, then it was similar to that well known phrase, From Daniel even unto Beersheba.

Wherefore it is said in the (e) book of the wars of the LORD, What he did in the Red sea, and in the brooks of Arnon,
(e) Which seems to be the book of the Judges, or as some think, a book which is lost.

Wherefore it is said in the book of the wars of the Lord,.... A history of wars in former times, which the Lord had suffered to be in the world; and which, as Aben Ezra thinks, reached from the times of Abraham and so might begin with the battle of the kings in his time, and take in others in later times, and particularly those of Sihon, king of the Amorites, and his conquests of some parts of Moab; and to this book, which might be written by some one of those nations, Moses refers in proof of what he here says:
what he did in the Red sea; that is, what Sihon king of the Amorites did, or the Lord by him, "at Vaheb in Suphah", as the words may be rendered; either against a king, or rather city, of Moab, whose name was Vaheb, in the borders of the land of Moab, or how he destroyed that city Vaheb with a storm or terrible assault (l):
and in the brooks of Arnon: some places situated on the streams of that river, which were taken by the Amorites from the Moabites, as the book quoted plainly testified.
(l) Vid. L'Empereur. Not. in Mosis Kimchi p. 195.

book of the wars of the Lord--A fragment or passage is here quoted from a poem or history of the wars of the Israelites, principally with a view to decide the position of Arnon.

The book of the wars of the Lord - This seems to have been some poem or narration of the wars and victories of the Lord, either by: or relating to the Israelites: which may be asserted without any prejudice to the integrity of the holy scripture, because this book doth not appear to have been written by a prophet, er to be designed for a part of the canon, which yet Moses might quote, as St. Paul doth some of the heathen poets. And as St. Luke assures us, that many did write an history of the things done, and said by Christ, Luke 1:1, whose writings were never received as canonical, the like may be conceived concerning this and some few other books mentioned in the old testament. The brooks - The brook, the plural number for the singular, as the plural number rivers is used concerning Jordan, Psalm 74:15, and concerning Tigris, Nahum 2:6, and concerning Euphrates, Psalm 137:1, all which may be to called because of the several little streams into which they were divided.