[2] According to the medieval Jewish scholar Rashi, "Sefer HaYashar" in this verse refers to the Pentateuch: Jacob's prophecy regarding Joshua's ancestor Ephraim—"His seed will fill the nations"[3]—was fulfilled when Joshua's victory gave him renown among the various nations who heard of the victory.
[4] According to the Book of Samuel, when David spoke his lament over the deaths of Saul and Jonathan, he began as follows: To teach the sons of Judah [the use of] the bow.
According to some other translations such as the English Standard Version “The Bow” (Hebrew: קָ֑שֶׁת, romanized: qāšeṯ) which David taught is hypothesised as a poetic lament over the deaths of Saul and Jonathan.
or most translations), verse 8:53 says that the preceding prayer of Solomon is written “in the book of song” (ἐν βιβλίῳ τῆς ᾠδῆς).
According to Alexander Rofeh, this suggests that the name Sefer HaYashar could be related to its function as a hymnal, and the second word might have originally been שיר (shir, "song") or ישיר (yashir, “he will sing”).