minhag - Line break before למען ירבו ימיכם

In most of my prayer books there is a line break before למען ירבו ימיכם in the second chapter of the Shema (see also this one from Vilna or Zhytomyr):

וְהָיָ֗ה אִם־שָׁמֹ֤עַ תִּשְׁמְעוּ֙ אֶל־מִצְוֺתַ֔י אֲשֶׁ֧ר אָֽנֹכִ֛י מְצַוֶּ֥ה אֶתְכֶ֖ם הַיּ֑וֹם לְאַֽהֲבָ֞ה אֶת־יְהוָ֤ה אֱלֹֽהֵיכֶם֙ וּלְעָבְד֔וֹ בְּכָל־לְבַבְכֶ֖ם וּבְכָל־נַפְשְׁכֶֽם׃ וְנָֽתַתִּ֧י מְטַֽר־אַרְצְכֶ֛ם בְּעִתּ֖וֹ יוֹרֶ֣ה וּמַלְק֑וֹשׁ וְאָֽסַפְתָּ֣ דְגָנֶ֔ךָ וְתִֽירֹשְׁךָ֖ וְיִצְהָרֶֽךָ׃ וְנָֽתַתִּ֛י עֵ֥שֶׂב בְּשָֽׂדְךָ֖ לִבְהֶמְתֶּ֑ךָ וְאָֽכַלְתָּ֖ וְשָׂבָֽעְתָּ׃ הִשָּֽׁמְר֣וּ לָכֶ֔ם פֶּ֥ן יִפְתֶּ֖ה לְבַבְכֶ֑ם וְסַרְתֶּ֗ם וַֽעֲבַדְתֶּם֙ אֱלֹהִ֣ים אֲחֵרִ֔ים וְהִשְׁתַּֽחֲוִיתֶ֖ם לָהֶֽם׃ וְחָרָ֨ה אַף־יְהוָ֜ה בָּכֶ֗ם וְעָצַ֤ר אֶת־הַשָּׁמַ֨יִם֙ וְלֹֽא־יִהְיֶ֣ה מָטָ֔ר וְהָ֣אֲדָמָ֔ה לֹ֥א תִתֵּ֖ן אֶת־יְבוּלָ֑הּ וַֽאֲבַדְתֶּ֣ם מְהֵרָ֗ה מֵעַל֙ הָאָ֣רֶץ הַטֹּבָ֔ה אֲשֶׁ֥ר יְהוָ֖ה נֹתֵ֥ן לָכֶֽם׃ וְשַׂמְתֶּם֙ אֶת־דְּבָרַ֣י אֵ֔לֶּה עַל־לְבַבְכֶ֖ם וְעַֽל־נַפְשְׁכֶ֑ם וּקְשַׁרְתֶּ֨ם אֹתָ֤ם לְאוֹת֙ עַל־יֶדְכֶ֔ם וְהָי֥וּ לְטֽוֹטָפֹ֖ת בֵּ֥ין עֵֽינֵיכֶֽם׃ וְלִמַּדְתֶּ֥ם אֹתָ֛ם אֶת־בְּנֵיכֶ֖ם לְדַבֵּ֣ר בָּ֑ם בְּשִׁבְתְּךָ֤ בְּבֵיתֶ֨ךָ֙ וּבְלֶכְתְּךָ֣ בַדֶּ֔רֶךְ וּֽבְשָׁכְבְּךָ֖ וּבְקוּמֶֽךָ׃ וּכְתַבְתָּ֛ם עַל־מְזוּז֥וֹת בֵּיתֶ֖ךָ וּבִשְׁעָרֶֽיךָ׃

לְמַ֨עַן יִרְבּ֤וּ יְמֵיכֶם֙ וִימֵ֣י בְנֵיכֶ֔ם עַ֚ל הָֽאֲדָמָ֔ה אֲשֶׁ֨ר נִשְׁבַּ֧ע יְהוָ֛ה לַאֲבֹֽתֵיכֶ֖ם לָתֵ֣ת לָהֶ֑ם כִּימֵ֥י הַשָּׁמַ֖יִם עַל־הָאָֽרֶץ׃

Although in Emden, Heidenheim and Artscroll there isn't, and it doesn't seem to be a general minhag for Böhmen-Mähren-Ungarn countries based on this machzor from Prague. In the Torah scroll there is no line break either. Where does this minhag come from and what is its meaning?

Answer

The issue is discussed in detail by R' Hamburger in Volume 4 of his priceless series, Shorshei Minhag Ashkenaz, and a bit shorther, but in English in the kitzur edition. His main point is that in Ashkenaz most Jews became unfamiliar with the proper melody of Torah reading over the centuries (see Orach Chayim 61:24), so they didn't read it anymore aloud and they also finished it earlier than the rabbi. As they were waiting for the rabbi, he started to read it aloud, and he had multiple reasons to do this. First of all, on Berakhot 12b, when the reading of the last paragraph in the evening is discussed, the mishnah uses the word remind (מזכירין) instead of remember (זוכרין). So by reading out aloud the last paragraph, he could remind the congregation of the Exodus, which is a positive commandment based on Devarim 16:3:

לֹֽא־תֹאכַ֤ל עָלָיו֙ חָמֵ֔ץ שִׁבְעַ֥ת יָמִ֛ים תֹּֽאכַל־עָלָ֥יו מַצּ֖וֹת לֶ֣חֶם עֹ֑נִי כִּ֣י בְחִפָּז֗וֹן יָצָ֨אתָ֙ מֵאֶ֣רֶץ מִצְרַ֔יִם לְמַ֣עַן תִּזְכֹּ֗ר אֶת־י֤וֹם צֵֽאתְךָ֙ מֵאֶ֣רֶץ מִצְרַ֔יִם כֹּ֖ל יְמֵ֥י חַיֶּֽיךָ׃

Thou shalt eat no leavened bread with it; seven days shalt thou eat unleavened bread therewith, even the bread of affliction; for in haste didst thou come forth out of the land of Egypt; that thou mayest remember the day when thou camest forth out of the land of Egypt all the days of thy life.

The exact meaning of all the days of your life is discussed in the well known mishnah and in the Haggadah. This explains well the recital of the last paragraph, but not the verse Devarim 11:21. However, this verse is of particular importance, because if someone errs during the recital of the Shema, but remembers that he has already said it, there is no need to return to the beginning of the paragraph (Berakhot 16a). Many rabbis considered this verse suitable to bless all the Jews that made the effort to come to the synagogue, and read it aloud. (While there were others that opposed this practice, saying he shouldn't have anything else in mind when fulfilling the commandment of reciting the Shema.) I would also add that the word למען in Devarim 16:3 can allude to Devarim 11:21.

The line break can hint that from this point on the rabbi reads the verses aloud, which is recorded in multiple places, such as in Divrei Kehilot by R' Geiger:

And the rabbi (and if he is not present in the synagogue it is upon the teachers from the leaders of the community to take his place) says aloud למען ירבו until אמת with the teamim.

On p. 5 of the Sefas Yisroel siddur it is also written:

.'הרב הקורא שמע בטעמים מרים קולו מ'למען ירבו' עד 'אמת

The rabbi, who reads Shema with the teamim raises his voice from למען ירבו until אמת.

It is also mentioned in the Hungarian Jewish Encyclopedia:

The rabbi recites this part of the [second] chapter aloud.