Two Sets of Five
While it is clear from the Torah that the Ten Plagues as a whole were directed at Paroh and Egypt, in only five of the Plagues – עָרֹב, דֶּבֶר, בָּרָד, חֹשֶׁךְ, בְּכוֹרוֹת – is it explicitly stated that Hashem distinguished between the Egyptians and the Israelites. In the other five plagues of דָם, צְפַרְדֵּעַ, כִּנִים, שְׁחִין, אַרְבֶּה, the Torah simply says that all of Egypt was stricken, leaving the commentators to debate whether in these plagues the Israelites and Goshen were affected as well.
Regardless of which position one adopts, one must account for the textual distinction between the two groups of plagues. If the Israelites, in fact, suffered along with the Egyptians in five of the Plagues, why would Hashem spare them from harm only in the other five? On the other hand, if the Israelites emerged unscathed from all of the Ten Plagues, why does the Torah differentiate between the Plagues and specify this miraculous phenomenon in only half of them?1
Ethnic or Geographic
Even among the five plagues in which the text records that Hashem discriminated, it is unclear whether this distinction was based on race or place. By the Plagues of דֶּבֶר, חֹשֶׁךְ, and בְּכוֹרוֹת, the Torah specifies that Hashem distinguished between the Israelite and Egyptian populations, while in the Plagues of עָרֹב and בָּרָד, the separation emphasized is between the lands of Egypt and Goshen.2
Is this subtle difference significant? Were there differences even between these five plagues themselves, and if so, why? Or is it merely that there was complete population segregation, with 100% of the Israelites and none of the Egyptians living in Goshen, and thus the Torah's two different formulations really have one and the same meaning?3 Either way, if a Hebrew found himself in Egypt proper when a plague touched down, was he also at risk? And conversely, was an Egyptian able to find refuge in the land of Goshen?
To Protect or to Prove
Of the five plagues in which there is explicit differentiation between the Israelites and Egyptians (or between Goshen and Egypt), it is only before the three plagues of עָרֹב, דֶּבֶר, and בְּכוֹרוֹת that this is noted in the warning delivered to Paroh.4 And of these three,5 it is only after דֶּבֶר that the Torah emphasizes and Paroh checks to ascertain that this differentiation, in fact, occurred.
Attempting to account for these additional distinctions between the various plagues leads us to perhaps the most fundamental question of all: What was the goal of the differentiation? Was it simply to shield the Israelites from harm, or was it to demonstrate to Paroh the existence and workings of Divine providence?6 Is it possible that there was a dual purpose or that there were variations between the objectives of the different plagues?