Hashem shall reign for all eternity: There are three opinions concerning the text at this point: 1) According to the Avudaram by repeating "Hashem shall reign..." we are signaling the end of the song "Az Yashir". According to this view, the following verse, Shmos 15:19, is not part of "Az Yashir" and therefore was not sung by Moses and Bnai Yisrael at the Red Sea. 2) According to the Mechilta, the next verse was sung by Moses and Bnai Yisrael at the crossing of the Red Sea and therefore is part of "Az Yashir". In his opinion the verses "Hashem shall reign for all eternity" and Hashem, His kingdom is established forever and ever, should not be recited. 3) The third opinion is a "combination" of both; "Hashem shall reign..." is an extra praise we add as is sometimes done in other places. Hashem, His kingdom is established forever and ever, is a commentary of that verse and is inserted to divide "Az Yashir" from the additional praises.
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