וַיִּקַּ֨ח מַקְל֜וֹ בְּיָד֗וֹ וַיִּבְחַר־ל֣וֹ חֲמִשָּׁ֣ה חַלֻּקֵֽי־אֲבָנִ֣ים ׀ מִן־הַנַּ֡חַל וַיָּ֣שֶׂם אֹ֠תָם בִּכְלִ֨י הָרֹעִ֧ים אֲשֶׁר־ל֛וֹ וּבַיַּלְק֖וּט וְקַלְּע֣וֹ בְיָד֑וֹ וַיִּגַּ֖שׁ אֶל־הַפְּלִשְׁתִּֽי׃
And he took his staff in his hand, and chose him five smooth stones out of the brook, and put them in the shepherd’s bag which he had, even in his scrip; and his sling was in his hand; and he drew near to the Philistine.
Ibn Ezra
בחלקי Among the smooth stones. Comp. חלוקי אבנים smooth stones (1 Sam. 17:40). Among the smooth stones of the stream is thy portion. They seek for smooth stones to shape them into idols.
Rabbeinu Bahya
According to Bereshit Rabbah 85,9, (slightly different wording) by returning these three pledges to Yehudah, Tamar’s offspring did indeed merit to secure for itself (at different times in history) all these three items. Concerning Zerubavel, the leader of the Jews returning from exile in Babylon, we read in Chagai 2,23: ”I will take you, My servant Zerubavel son of Shaltiel- declares the Lord,- and make you as a signet for I have chosen you.” As to the פתיל, Tamar, as the mother of Peretz, became the ancestor of Betzalel, architect of the Tabernacle of whom it is written in Exodus 39,3 וקצץ פתילים, “he cut threads.” The word מטך was an allusion to King David of whom Samuel I 17,40 recorded that ויקח מקלו בידו, “he took his staff in his hand.”