There are several significant shifts of number in this week’s portion. One occurs earlier in the portion, when “Egypt” and “the Egyptians” chase the Israelites.
In Shemot/Exodus 14:9, the Egyptians are plural and take a plural verb:
Va-yirdefu Mitzrayim achareihem [The Egyptians set out after them]
In the next verse, however, the Israelites view “Egypt” as a singular entity traveling — nosea [singular] — after them.
Alan Lew writes in Be Still and Get Going:*
Why does the Torah shift number so cavalierly here? According to Rashi, it is because the Torah wishes to emphasize what it was the Israelites saw when they raised their eyes to the horizon. They saw not the Egyptians themselves, in the plural, but the spirit of Egypt, in the singular. They saw their idea of Egypt. They saw the Egypt in which they had cowered as slaves for four hundred years, in which they were abused and outnumbered. In other words, they saw their fear of Egypt. They saw a mental construct, or in Rebbe Nachman’s words, something that they were afraid of but didn’t have to be.
The biblical text takes pains to make the same point. This text is ambiguous about exactly how many chariots there were in the army that had pinned the Israelites down at the sea….
…Why would such a tremendous throng be afraid of 1,800, or even 180,000, charioteers? The answer is that they were not responding to what was really there, nor even to what they saw. Rather they were responding to a phantom. They were responding to a fear-inducing product of their own imagination.
Later, at the Song of the Sea — when Moses and then Miriam sing to the LORD — there is another shift:
Ashira L’YHVH — I will sing to the LORD (Exodus/Shemot 15:1)
Shiru L’YHVH — Sing [plural] to the LORD (15:21)
*For complete citation and other information, please see Source Materials.