When the Israelites left Egypt, they initially did so “with hand held high” (Exod 14:8), that is, proudly, defiantly. But then Pharaoh changed his mind. After having told the Israelites that they were free to go, he came to his senses: “What have we done, freeing Israel from serving us?” He immediately dispatched his army to go after the Israelites, and it was not long before the troops caught up with the Israelites camped on the shore of the Red Sea. Seeing the approaching army, the people panicked: where could they go now, trapped between the Egyptian troops and the Sea?
At this point, an angel, who had apparently been inside the pillar of cloud/fire that led the Israelites on their way out of Egypt, moved the pillar to the space between them and the Egyptians, thereby temporarily preventing the latter from attacking. As a result, the Torah says, “this one [that is, the Egyptian camp] did not approach that one the whole night” (Exod 14:20).
In connection with this verse is a midrash attributed to various sages (see b. Megillah 10b and parallels), according to which at that moment the Holy One reproved the angels who usually sing before the heavenly throne: “My creatures are about to drown in the sea and you are singing?” The comment seems odd: where did our parashah anything about angels singing?
It all has to do with the precise wording of the verse mentioned above, “this one [that is, the Egyptian camp] did not approach that one the whole night.” In Hebrew the phrase velo karav zeh el zeh (“this one did not approach that one”) is reminiscent of a phrase that occurs in the prophet Isaiah’s vision of the heavenly throne (Isaiah chapter 6). There, the seraphim (apparently some sort of angel) “called one to another (kara zeh el zeh) Holy, Holy, Holy is the Lord of Hosts! His glory fills the whole earth” (Isa 6:3). Perhaps, this midrash proposes, the phrase in Exodus velo karav zeh el zeh is meant to refer to these same angels. On any other day they call “one to another” to sing God’s praises, but on that particular day, with the Israelites trapped on the edge of the Red Sea, God stopped them. “My creatures are about to drown in the sea and you are singing?”
As scholars have shown, in the process of transmission this midrash came to be changed: instead of applying to the trapped Israelites, it was taken to refer to a later stage of the exodus account, when the pursuing Egyptians were drowned in the waters of the Sea. The Israelites, having thus been saved, sang a song of thanksgiving to God (Exodus 15), but when the angels sought to join in, God reproved them: “My creatures [here understood as the Egyptians] are drowning in the Sea and you are uttering praises?” This is a wonderfully universal message: even the Egyptian soldiers are God’s “creatures” and, while the Israelites understandably rejoiced at having been saved, the angels should not have tried to join in. But such a context does not fit the original verse on which this midrash depends: “this one did not approach that one” refers to when the Israelites were in danger of drowning, not the Egyptians.
Note: This fact was pointed out (apparently independently) by Rabbi M. Kasher and Professor Joseph Heinemann; the matter was subsequently explored at length by Prof. David Henschke in Akdamut 6, 59-68 (Hebrew), available on-line at: http://www.bmj.org.il/files/591294582533.pdf. Speakers of modern Hebrew are likely to be confused by the grammatical form of the verb in ma’asei yadai tove‘im bayam: in Mishnaic Hebrew, this “participle” regularly refers to both present and future events, hence “are about to drawn” could also be understood as “are [now] drowning.” The phrase amar shirah (as well as the rarer amar himnon) in Mishnaic Hebrew means to offer thanksgiving, but both phrases suggest thanksgiving that was sung, hence the simple translation “sing.”