“And G-d took us out of Egypt with a strong hand and an outstretched arm” (D’varim 26:8). The Hagaddah tells us that “with a strong hand” refers to the plague of pestilence, which was the fifth plague, and that “an outstretched arm” refers to the “sword” G-d used to kill the Egyptians, quoting verses that prove that each of those terms means those things. That G-d is described as having/using a “strong hand” and “an outstretched arm” to take us out of Egypt is well attested (see, for example, D’varim 4:34 and 5:15). However, it is unclear what this “sword” refers to, and why it is specifically the plague of “dever” (pestilence) that is referred to as G-d’s “strong hand.”
Several commentators (e.g. Shibolay Haleket and Orchos Chayim) reference the Midrash (Sh’mos Rabbah 10:2, Midrash T’hillim 78:16) that says that “dever” accompanied every plague. The easiest way to understand this Midrash is by applying the way some (e.g. Unkoles, Sh’mos 9:3 and Radak, shoresh D-B-R) translate the word “dever,” connoting death in general rather than a deadly malady. The focus of the fifth plague was the death of the Egyptian’s animals, hence it was called “dever,” while the focus of the other plagues (with the exception of the tenth plague, which will be discussed shortly) was the damage they did, not the deaths they caused in the process. When the Haggadah tells us that the “strong hand” in the verse refers to “dever,” it is therefore referring to the deaths caused by all the plagues, not just the death of the animals in the fifth one.
If G-d’s “strong hand” refers to all the plagues, the “sword” that G-d’s “outstretched arm” refers to must not be the death of the first born, as that was the tenth plague, and would have already been included in G-d’s “strong hand.” Many explain this “sword” as referring to the civil war that broke out after the firstborn heard what the tenth plague will be, with many Egyptians being killed when the firstborn tried to force the rest of the Egyptians to let Israel go so that they wouldn’t be killed in the tenth plague. Being that these deaths were not by G-d’s hand, but were an extension of what G-d had already done along with the mere threat of another plague, it was referred to as His “outstretched arm.” Nevertheless, it is still possible for the “sword” to refer to the death of the firstborn, even if the deaths caused by all the plagues are referred to as G-d’s “strong hand,” and would therefore not be included in His “outstretched arm.”
The firstborn weren’t the only Egyptians killed in the tenth plague, as many other Egyptians died due to collateral damage (which is why the Children of Israel were warned to stay inside, in order to avoid being victims of this collateral damage, see Sh’mos 12:22). This is also why the Egyptians were afraid that they were all going to die, not just the firstborn (see Rashi on Sh’mos 12:33; Akeidas Yitzchok understands the “sword” of G-d’s “outstretched arm” to be referring to those non-firstborn Egyptians who died during the tenth plague). If the “dever” meant by G-d’s “strong hand” refers to those who died during all the plagues, since the first nine plagues were not plagues of (human) death, the deaths “dever” refers to in the tenth plague must also be of those who died as a byproduct of the plague. (For the fifth plague, it would mean those humans who died as a result of the pestilence that was directed at the animals.) For the tenth plague, then, since it would also refer to those who died as a byproduct of the plague even though they were not the primary target, it would mean the non-firstborn who died when the firstborn were smitten. This would allow the firstborn to be the ones who died via G-d’s “outstretched arm,” i.e. by the “sword” (directly), rather than via His “strong hand” (indirectly) even if some of the deaths that occurred during the tenth plague were victims of G-d’s “strong hand.”
Categorizing all who died in the plagues as being victims of G-d’s “strong hand” and “outstretched arm” fits very well with Moshe’s initial warning to Pharaoh, that he better let Israel go or G-d will smite them (referring to the Egyptians, even though Moshe was being polite by colloquially referring to his own people) “by pestilence (dever) or by the sword” (Sh’mos 5:3, see Rashi), as these terms encompass the deaths caused by all ten plagues. But there’s another way to include all ten plagues in these expressions just as effectively.
Netziv (Ma’aseh Nisim) says that the reason the word “hand” is used for the fifth plague is that each individual plague is said to be from “G-d’s finger” (see Sh’mos 8:15), so after five “fingers” (plagues) we have a “hand.” When Pharaoh didn’t give in after the first five plagues it was of his own volition, whereas for the last five (which he says also constitutes a “hand”) G-d “hardened/strengthened his heart.” Therefore, the first “hand” is referred to as G-d’s “strong hand,” as it showed His strength (or at least a measure of it) while allowing Pharaoh to respond to it, while the second “hand,” which Pharaoh was forced to endure no matter what, is referred to as G-d’s “outstretched arm,” as it was definitely going to stay “outstretched” at least until after the last five plagues had been sent. [Obviously Netziv is understanding Pharaoh’s heart being hardened as his no longer having a choice, as opposed to G-d giving him back the ability to really choose despite the plagues, see S’fornu on Sh’mos 4:21 and 9:35.]
Although I described G-d’s “outstretched arm” a little differently than Netziv actually does (he quotes and applies a Zohar), the idea is basically the same. The bottom line is that each of these two expressions refers to five of the plagues, not just one, so G-d’s “strong hand” is not limited to just the fifth plague, and His “outstretched arm“ refers to the inevitability of the last five plagues (once Pharaoh didn‘t give in after the first five). Moshe’s warning to Pharaoh can be explained in a similar way as the first approach; if he doesn’t let the Children of Israel go he will suffer through the five plagues referred to as G-d’s “strong hand” (with “dever,” pestilence, being the fifth “finger” that completes the “hand”) and the five plagues that are referred to as His “outstretched arm” (symbolized by a “sword” that is ready to strike).
Netziv’s approach also allows us to understand another verse that the commentators struggle with. At the burning bush, G-d told Moshe that Pharaoh wouldn’t listen, “not even after being hit with a strong hand” (Sh’mos 3:19). Since one of the things that facilitated our exodus from Egypt was G-d’s “strong hand” (as the verse we started with explicitly says), how could G-d tell Moshe that His “strong hand” won’t work? (Most commentators therefore explain the verse to mean that Pharaoh won’t listen “until G-d uses His strong hand,” see Rashi.) Based on the Netziv, the verse can be read in a much more straightforward manner; even after the first five plagues, which are referred to as G-d’s “strong hand,” Pharaoh won’t give in. These plagues were still an important component of the exodus, teaching everyone about G-d and His might, and if not for the first five plagues, Pharaoh wouldn’t have given in after the sixth plague even if G-d hadn’t hardened his heart. But the first five plagues alone weren’t enough, so when G-d told Moshe that Pharaoh wouldn’t give in right away, He added that he won’t give in even after being shown G-d’s “strong hand.”
[It is true that a later verse (6:1) implies that Pharaoh will send them out because of G-d’s “strong arm,” and it would be a stretch to suggest that the strong arm mentioned in this verse refers to how desperate Pharaoh will be for them to leave, to the point that he will “strong arm” them to leave faster than they otherwise would have. (This is especially true if the terms “strong arm” and “outstretched arm” are purposely used to counter the use of those expressions to describe the self-promoted strength/divinity of Pharaoh, see http://mosaicmagazine.com/essay/2015/03/was-there-an-exodus/, as using them to describe Pharaoh would strongly undermine that. As an aside, the use of the terms in Yechezkel (20:33-34) to describe what G-d might do to us doesn’t disprove that theory, as it was a threat directed against those who now associated those terms with what G-d did to the Egyptians.) Nevertheless, since the context of that verse is a rebuke of Moshe for not seeing the bigger picture and becoming discouraged because of things seemed to have gotten worse, G-d could have been pointing out that even though it looks like speaking to Pharaoh didn’t accomplish anything, it was a necessary preparatory step in the redemption process, just as the “strong hand” He will use against Pharaoh won’t seem to work at first even though it greatly impacted the eventual outcome.]
