Albert Barnes Commentary 2 Samuel 1:18

"(and he bade them teach the children of Judah [the song of] the bow: behold, it is written in the book of Jashar):" — 2 Samuel 1:18 (ASV)

The use of the bow - Omit “the use of.” “The bow” is the name by which this dirge was known, so called from the mention of Jonathan’s bow in 2 Samuel 1:22. The sense would then be: And he commanded them to teach the children of Israel the song called Kasheth (the bow); that is, he gave directions that the song should be learned by heart .

It has been further suggested that in the Book of Jasher there was, among other things, a collection of poems in which special mention was made of the bow. This was one of them; 1 Samuel 2:1–10 was another; Numbers 21:27–30 was another; Lamentations 2 was another; Lamentations 3 was another; Jacob’s blessing (Genesis 49); Moses’ song (Deuteronomy 32); perhaps his blessing (Deuteronomy 33; see 2 Samuel 1:29); and such psalms as Psalms 44, Psalms 46:1–11, Psalms 76:1–12, and so on. Habakkuk 3 and Zechariah 9:9-17 also belonged to it.

The title by which all the poems in this collection were distinguished was קשׁת qesheth, “the bow.” Therefore, when the writer of 2 Samuel transferred this dirge from the Book of Jasher to his own pages, he transferred it with its title, just as we might do with any of the Psalms.

The book of Jasher - See the marginal reference note.