Midrasch zu Tehillim 77:17

..."And the waters were a wall for them" Made them as a type of wall. "On their right and on their left" On their right due to the merit of the Torah that they would in the future receive through the right, as it is said "From His right, a fiery law to them" (Deut. 33:2). And on their left: this is prayer.

(Exodus 14:21) "and He made the sea into dry land and the waters were split." All the waters in the world were thus rendered. And whence do you derive (the same for) waters in pits, and in cavities, and in caves and in pitchers and in cups and in casks and in glasses? From "and the waters were split." Is it not already written "and He made the sea into dry land"? We are hereby apprised that all the waters in the world were split. And whence do you derive (the same for) the upper and the lower waters and the depths? From (Psalms 77:17) "The waters saw You, O G d; the waters saw You and quaked. The depths quaked as well." "The waters saw You" — These are the waters crossed by Israel, which dried up at the word of the Holy One Blessed be He, viz. (Ibid. 114:3) "The sea saw and fled." "the waters saw You and quaked" — These are the upper waters. "The depths quaked as well" — These are the lower waters. And thus is it written (Ibid. 77:18) "Clouds streamed water; the heavens rumbled" — These are the upper waters. (Ibid.) "Your gravels, too, went out" — These are the lower waters. And it is written (Habakkuk 3:10) "The depths have raised their voice, etc." And when they (the waters of the Red Sea) returned to their place, all the waters of the world followed suit, as it is written (Exodus 14:28) "And the waters returned" — All of the waters in the world returned to their places.

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