When thou takest the sum of the children of Israel (Exod. 30:12). R. Yosé the son of Hanina said: This verse indicated to him that in the future he would bring the first of the tribes to the Shekhinah. But which one was the first tribe? It is Reuben, as it is said: Let Reuben live and not die (Deut. 33:6). This is what is meant by Thou liftest up the head (rosh) of the children of Israel; i.e. he lifted up the first (rishon) of the tribes.
כִּי תִשָּׂא אֶת רֹאשׁ. אָמַר רַבִּי יוֹסִי בַּר חֲנִינָא: רְמָזוֹ שֶׁהוּא עָתִיד לְקָרֵב רִאשׁוֹן שֶׁל שְׁבָטִים לַשְּׁכִינָה. וְאֵי זֶהוּ? זֶה רְאוּבֵן, שֶׁנֶּאֱמַר: יְחִי רְאוּבֵן וְאַל יָמֹת (דברים לג, ו). וְזֶהוּ כִּי תִשָּׂא אֶת רֹאשׁ בְּנֵי יִשְׂרָאֵל, רִאשׁוֹן שֶׁל שְׁבָטִים.
When thou takest the sum of the children of Israel (Exod. 30:12). R. Yosé the son of Hanina said: This verse indicated to him that in the future he would bring the first of the tribes to the Shekhinah. But which one was the first tribe? It is Reuben, as it is said: Let Reuben live and not die (Deut. 33:6). This is what is meant by Thou liftest up the head (rosh) of the children of Israel; i.e. he lifted up the first (rishon) of the tribes.