This week’s parsha starts the 10 plagues. As we know, Rabbi Yehuda has a mnemonic that divides them into three groups:
Much has been said about this, but one way to look at this is to note that ה׳ gives each of the three groups a different pedagogical purpose:
Before מכת דם:
Before מכת ערוב:
Before מכת ברד:
בזאת תדע כי אני ה׳, the first מכות, were about demonstrating that ה׳ exists. Pharaoh initially denied this:
And ה׳ does that by demonstrating that other “gods” do not exist. ה׳ starts with the Nile, worshipped as a god.
The Nile is the lifeblood of Egypt. The irony is that ה׳ makes that literal, and destroys the Nile and all it symbolizes.
The next plague deals with Pharaoh, who claimed to be a god, symbolized by the Nile crocodile.
We think of frogs as cute and harmless (“Frogs in his bed and frogs on his head”) but that’s a mistranslation of צפרדע.
Again, ה׳ is ironically destroying the gods of Egypt: you think you are the mighty crocodile? I’ll show you real crocodiles.
But the last of the three, כנים, is less serious and isn’t directed at Egyptian gods:
This was a plague aimed not at the gods of Egypt, but those who claim to be able to manipulate them, חרטמים.
We’ve seen these חרטמים throughout the story so far:
And חז״ל say that their “power” was to manipulate שדים.
What is a שד? It’s part of a way of looking at the world, that acknowleges that there are invisible forces that affect us, and that those forces could be controlled if we understood them.
The מעשה שדים perspective is not scientific in the modern sense, but it is technological. Human beings can discover the laws that run the universe and hack them for our own purposes. So what happened in מכת כינים?
Why would a שד be unable to control small things? The size of a barley corn, כשעורה, is the smallest halachically defined size.
So the sequence of lessons of בזאת תדע כי אני ה׳ is:
A physical thing, the Nile, can be a god—nope.
Human beings, Pharaoh, can be a god—nope.
Finally, human beings can control the gods—nope, because there is only one G-d and there are limits to what the forces that human beings can control can do. כשעורה is symbolic of the Planck length of the universe.
אצבע אלקים הוא is an admission of the limitations of the חרטמים in the face of, as it were, ה׳'s fine motor skills.
Here, the חרטמים are forced to experience יראת ה׳ not in the infinite expanse of the universe, but in the infinitesimal.
And with that, ה׳ moves on to the next lesson: למען תדע כי אני ה׳ בקרב הארץ.