The book of the wars, &c. An ancient book, which, like several others quoted in Scripture, has been lost. (Challoner)

St. Augustine (q. 42) thinks this book was written by one of that country. Others believe that Moses wrote a more detailed account of the wars which he had to wage with the Amalecites, (Exodus xvii. 14,) and these other nations, out of which he has only inserted some of the heads in the Pentateuch. But whether these two verses were taken from another work of Moses, or from the history of some other person, they are now of divine authority. Saul says to David, (1 Kings xviii. 17,) fight the battles of the Lord,....and the children of God and of Ruben pass all armed for war before the Lord, (chap xxxii. 29.; Calmet) whence it appears, that the wars of the Hebrews were attributed to God. Tostat is of opinion, that the Book of the Just, is the same with that to which Moses here refers. See Josue x. 13., and 2 Kings i. 18. But Theodoret thinks rather, that the former was a more extensive account of the transactions of Josue, out of which the book which bears his name was compiled. Such records certainly existed, to which the sacred historians frequently refer: and it is very probable, that a work of this nature was compiled in the days of Moses, or perhaps before his time. (St. Augustine, City of God xviii.) As it contained a prediction, respecting the future wars, in which the Hebrews were about to engage, it could not but make a suitable impression upon them. It might already be in every one’s mouth, and the Hebrew may insinuate, that it would be handed down to the latest posterity: “Wherefore in the history, or account of the wars of the Lord, this also shall be mentioned,” jamor, dicetur. According to this interpretation, it would not be necessary to suppose, that Moses refers to any more ancient book, as sepher means also, “a narration” by word of mouth; and Rabbi Menachem believes, that God had revealed this event to Moses, encouraging him with the assurance, that he would give him the victory over the nations bordering upon the Arnon, as he had done over the Egyptians and Amalecites at the Red Sea. See Sixt. Senens. (Haydock)

Of Arnon, the waters of which are supposed to have given the Hebrews a passage, as the Chaldean asserts on the authority of Psalm lxxiii. 15. Habacuc (iii. 13) also mentions that several rivers were dried up by God. The Hebrew text is almost unintelligible, “From, or against, Vaheb to Supha.” As there is no verb, some translate, “he (Sehon) fought against Vaheb (Grotius reads Moab) at Supha, or he came to Veb.“ Some render this word, he made, “a whirlpool in the torrents of Arnon.” But Calmet would substitute Zared instead of Vaheb: “The encamped at the torrent of Zared, and came to Supha, (Deuteronomy i. 1, where we read the Red Sea) to the torrent of Arnon.” Protestants translate, “What he did in the Red Sea, and in the brooks of Arnon, (16) and at the stream of the brooks that goeth down to the dwelling of Ar, and lieth upon the border of Moab.” (Haydock)