Albert Barnes Commentary Job 39:23

"The quiver rattleth against him, The flashing spear and the javelin." — Job 39:23 (ASV)

The quiver rattles against him - The quiver was a case made for containing arrows. It was usually slung over the shoulder so that it could be easily reached to draw out an arrow.

Warriors on horseback, as well as on foot, fought with bows and arrows, as well as with swords and spears. The idea here is that the war-horse carried these instruments of war.

The rattling of the quiver was caused by the fact that the arrows were thrown somewhat loosely into the case or quiver and that in the rapid motion of the warrior they were shaken against each other. Thus, Virgil, Aeneid 9.660:

pharetramque fuga sensere sonantem.

Silius, Book 12:

Plena tenet et resonante pharetra.

And again:

Turba ruunt stridentque sagittiferi coryti.

So Homer (Iliad, Book 1), when speaking of Apollo:

Τόξ ὤμοισιν ἔχων, ἀμφηρεφέα τε φαρέτρην
Ἔκλαγξαν δ ̓ ἄῤ ὀΐστοὶ ἐπ ̓ ὤμων χωομένοιο.

Tox́ ōmoisin echōn, amfērefea te faretrēn
Eklangxan d' aŕ oistoi ep' ōmōn chōmenoio.

See Scheuchzer’s “Phys. Sac., in loc.”