Verse 40: And he took his staff in his hand, and chose him five smooth stones out of the brook (or, valley), and put them in a shepherd’s bag (Heb. vessel) which he had, even in a scrip; and his sling was in his hand: and he drew near to the Philistine.
[And he took his staff] That is, which previously he was wont to carry (Vatablus). The arms of shepherds are the rod, and the crook, and those wherewith they might fight at a distance, the bow, arrows, slings, and stones (Bochart’s A Sacred Catalogue of Animals 1:2:44:458). He preferred to be seen as a shepherd, rather than a soldier, so that the glory might be ascribed to divine, not human, power (Sanchez).
His staff; his shepherd’s staff. These arms were in themselves contemptible, yet chosen by David; partly, because he had no skill to use other arms; partly, because he had inward assurance of the victory, even by these weapons; and partly, because such a conquest would be most honourable to God, and most shameful and discouraging to the Philistines.
[He chose for himself five completely clear stones, חַלֻּקֵי־אֲבָנִים] חַלֻּקֵי is not found elsewhere. חָלַק signifies two things: 1. to divide up; 2. to be smooth, slippery, hairless. All the Interpreters that I saw follow the latter signification here; indeed, they maintain that it is an adjective, the smooth of stones (Dieu); that is, of the lævibus/smooth stones (but read levibus/smooth, because in Greek it is λεῖος/smooth, not λαῖος), which sort of syntax is in that, the black of fleeces. A Genitive of the whole, or posited partitively (Piscator). Smooth stones (Septuagint, Montanus, Junius and Tremellius, Vatablus), without protrusion (Strigelius, Vatablus), polished (Munster), that is, round and not sharp (Vatablus): which are able easily to be cast out of a sling, and more certainly to be conducted to their intended target (Sanchez). Others make it substantive, smoothnesses of stones (thus Jonathan); by hypallage, in the place of stones of smoothnesses, that is, extremely smooth (Dieu). Slipperinesses of stones; that is, slippery stones: For the former, out of two placed in a construct chain, is often a substantive in the place of an adjective; thus in 2 Kings 19:23, I will cut down קוֹמַ֤ת אֲרָזָיו֙ מִבְח֣וֹר בְּרֹשָׁ֔יו, the height of the cedars thereof, the choice of the firs thereof, that is, the tall cedars thereof, the most excellent firs thereof (Glassius’ “Grammar” 29). Everyone sees that these things are somewhat harsh; apart from the fact that smooth stones, and each one polished, do not appear quite so apt for this matter, as stones jagged, broken, and having sharp projections, which are thrust into the forehead far more easily and certainly; I do not see why we do not rather follow the first signification of the term, and translate it, parts, or rather partitions, or divisions, of stones; five broken, not whole, stone; so that it might be the same as חֶלְקֵי־אֲבָנִים, portions of stones, just as it could be read, if the text were without points. Near to this is the passage in Isaiah 57:6, בְּחַלְּקֵי־נַ֣חַל חֶלְקֵ֔ךְ, among the smooth of the stream is thy portion, which they also translate, among the smooth of the stream; that is among the smooth stones. But I translate it, among the divisions of the stream; that is, the rivulets into which the stream divides itself (Dieu). [See the additional things to be noted, Lord willing, on that passage.]
[Out of the brook (thus Junius, Piscator, Malvenda)] Or, out of the valley (Junius, Piscator) [thus most interpreters], out of the arena (Arabic, Syriac). He arms himself with five stones, so that, if he should err in the first strike, he might make use of the others for repeated strikes (Hostus’ Concerning the Duel of David and Goliath 10).
Chose him five smooth stones, that if one should fail him, he might make use of another. Smooth stones, because such stones would go most freely out of the sling; and consequently, with more force and certainty, directly to the mark which he aimed at.
[Into a satchel, etc., בִּכְלִ֙י הָרֹעִ֧ים אֲשֶׁר־ל֛וֹ וּבַיַּלְק֖וּט] In the vessel (instrument [Tigurinus]) of shepherds, which was to him, and in a satchel (Montanus). Within the pastoral satchel, and within the case of the sling (Munster), in which a stone was stored for spinning and casting (Malvenda). In the pastoral instrument, which he had, that is, in a satchel (Jonathan, Pagnine, Junius and Tremellius, Vatablus, similarly the Syriac, Dutch, English, Glassius). The copula ו/and sometimes signifies, that is. Thus in 1 Samuel 28:3, and they buried him in Rama, וּבְעִירוֹ, that is, in his own city. Thus in 2 Samuel 17:12. Thus in Genesis 35:12, to thee will I give it, וּלְזַרְעֲךָ, that is, to thy seed, as in Acts 7:5. In Leviticus 5:1, if a soul sin, וְשָׁמְעָה, that is, hear the voice of swearing. In Numbers 31:6, and the holy instruments, וַחֲצֹצְרוֹת, that is, the trumpets of sounding in his hand (Glassius’ “Grammar” 691). Some maintain that there were two vessels here. Thus I translate it, he put them in a shepherd’s vessel, or pouch, or satchel, and in a gathering, understanding, of his garment, or in a garment set back. Thus among the ancient monuments of stone there is to behold a Roman slinger, who in his cloak, or mantle set back, carries stones in his bosom. Thus David put stones in both places, so that they might be more ready to hand. Others think that יַלְקוּט/yalkut/scrip was a singular box designed for collecting stones. This word is not found anywhere else in Scripture (Malvenda).
[He carried his sling in his hand] Now, no one is ignorant that there were slingers serving as soldiers in all the battles of the ancients, Vegetius’ Military Institutions of the Romans 1:6, where are also many other things to the praise of slings (Grotius). See Virgil’s Æneid 9, the whistling sling…; and Diodorus Siculus’ Historical Library 6, concerning the use, and expertise, of the sling in the Balearic islands; Livy’s Decades 8:4, where he relates that the slingers were so skilled, that they, being well-practiced, cast round stones through circles of small circumference at a great distance: and they wounded not only the heads of enemies, but whatever part of the face they aimed at. Among the Israelites, the use of the sling was common, and the skill was also admirable. See Judges 20:16 [on which place you will find a great many things brought together]. It certain requires great skill, to be able certainly to hit an immobile target: but it is far more admirable to strike a mobile target, even the forehead of a man advancing at a rapid pace (Hostus’ Concerning the Duel of David and Goliath 10).
His sling was in his hand: The sling was a sort of weapon not unusual in the fights of ancient times, and many arrived at great dexterity of slinging stones with great certainty; of which we have instances both in Scripture, as Judges 20:16, and in Diodorus Siculus, and Livy, and other authors.
Verse 41: And the Philistine came on and drew near unto David; and the man that bare the shield went before him.
[He was going, advancing] It signifies an haughty advance, as if he were proceeding to nuptials and triumph (Sanchez).
 Hebrew: וַיִּקַּ֙ח מַקְל֜וֹ בְּיָד֗וֹ וַיִּבְחַר־ל֣וֹ חֲמִשָּׁ֣ה חַלֻּקֵֽי־אֲבָנִ֣ים׀ מִן־הַנַּ֡חַל וַיָּ֣שֶׂם אֹ֠תָם בִּכְלִ֙י הָרֹעִ֧ים אֲשֶׁר־ל֛וֹ וּבַיַּלְק֖וּט וְקַלְּע֣וֹ בְיָד֑וֹ וַיִּגַּ֖שׁ אֶל־הַפְּלִשְׁתִּֽי׃  Hebrew: הַנַּחַל.  Hebrew: בִּכְלִי.  Pliny’s Natural History 8:48:73:193.  That is, a transposition of the natural relation of two elements in a proposition.  Hebrew: מִן־הַנַּחַל.  2 Samuel 17:12: “So shall we come upon him in some place where he shall be found, and we will light upon him (וְנַ֣חְנוּ עָלָ֔יו, that is, we upon him) as the dew falleth on the ground: and of him and of all the men that are with him there shall not be left so much as one.”  Publius Flavius Vegetius Renatus was a fourth century author. He wrote Military Institutions of the Romans (De Re Militari).  The Balearic Islands are off the eastern coast of Spain. The inhabitants were famous for their skill with the sling, and served both the Carthaginians, and later the Romans, as mercenaries.  Hebrew: וַיֵּ֙לֶךְ֙ הַפְּלִשְׁתִּ֔י הֹלֵ֥ךְ וְקָרֵ֖ב אֶל־דָּוִ֑ד וְהָאִ֛ישׁ נֹשֵׂ֥א הַצִּנָּ֖ה לְפָנָֽיו׃