זִכְר֤וּ לְעוֹלָם֙ בְּרִית֔וֹ דָּבָ֥ר צִוָּ֖ה לְאֶ֥לֶף דּֽוֹר׃
Erinnere dich für immer an seinen Bund, das Wort, das er tausend Generationen geboten hat;
Rashi
Quivers. Quivers in which they place arrows, as in, “Prepare the arrows, fill the quivers הַשְּׁלָטִים,”29I.e. Teaching [אלף] the Torah acts as a shield [המגן]. and it corresponds to the Chamber of Hewn Stone, from where instruction goes forth, for the Torah act as a shield to Yisroel.30I Divrei Hayamim 16:15. It is also possible to render that אֶלֶף הַמָּגֵן is the same as מָגֵן הָאֶלֶף, the shield of the thousand, alluding to, “the word [of the Torah] He commanded for a thousand generations.”31Alternatively, שלטי are shields. (Metzudas Tzion)