בָּעֵ֣ת הַהִ֗יא יִקְרְא֤וּ לִירוּשָׁלִַ֙ם֙ כִּסֵּ֣א יְהוָ֔ה וְנִקְוּ֨וּ אֵלֶ֧יהָ כָֽל־הַגּוֹיִ֛ם לְשֵׁ֥ם יְהוָ֖ה לִירוּשָׁלִָ֑ם וְלֹא־יֵלְכ֣וּ ע֔וֹד אַחֲרֵ֕י שְׁרִר֖וּת לִבָּ֥ם הָרָֽע׃ (ס)
אין יענער צײַט װעט מען רופֿן ירושָלַיִם דער טראָן פֿון גאָט, און אײַנזאַמלען װעלן זיך צו איר אַלע פֿעלקער, פֿון װעגן גאָטס נאָמען, קײן ירושָלַיִם, און זײ װעלן מער ניט גײן נאָך דער אײַנגעשפּאַרטיקײט פֿון זײער בײזן האַרצן.
Rashi
וַיִנָּהוּ' is an expression of drawing; in Aramaic, 'תִּתְּנֵהוּ לְפוּלְחָנִי' [they were drawn after My worship]. And similarly 'וְלֹא נֹהַּ בָּהֶם' it is no use to attract them to good.1 Yechezkeil 7:11. Menachem classifies 'וַיִנָּהוּ' as an expression of lamentation, as in 'נְהִי נִהְיָה' [a lament has come to be].2Michoh 2:4. And similarly 'וְלֹא נֹהַּ בָּהֶם' [is rendered as, 'and they will have no remorse']. And the meaning of 'וַיִנָּהוּ אַחֲרֵי ה' is, "they lamented their evil deeds, and returned after 'ה." Another explanation is that 'וַיִנָּהוּ' means 'and they gathered,' as in, "And all the nations will be gathered into it [Yerusholayim]"3Yirmiyohu 3:17. which the Targum renders, "And all nations will gather into it to worship." In this manner, the verse 'וְלֹא נֹהַּ בָּהֶם' may be rendered לֹא מֵהֶם "neither from them," וְלֹא מֵהֲמוֹנָם "nor from their multitude וְלֹא [מִ]נֹהַּ [שֶׁ]בָּהֶם meaning nor from their gathering.
Radak
ויאמר אלוקים יקוו המים מתחת השמים, the words מתחת השמים refer to the waters beneath the rakia, known as shamayim.
Ibn Ezra
The explanation of "let them be gathered" is: "let them join together", and likewise: "[and all the nations] shall be gathered to her [Jerusalem] Jeremiah 3:17