The ten plagues are presented in the Torah in two groups: seven are described in Parashat Va'eira and three are described in Parashat Bo.

Seven is the number of the midot, or emotional attributes of the heart, with which man is endowed; there are three aspects of intellect. Shem miShmuel explains that the first set of seven plagues corresponds to the heart and the second set of three plagues corresponds to the intellect. Each one of the plagues was intended to rectify and elevate one of those attributes and transform it into a G‑dly characteristic.

Emotions can be either good or bad...

Emotions can be either good or bad; the Egyptian motives were bad. Therefore, the first seven plagues came from a negative spiritual source. Blood, frogs, lice, wild animals, pestilence, boils, and hail are all creations which the Torah either forbids the Jews to ingest or consider impure. The fact that the Torah puts them out of our reach indicates that they cannot be elevated by man. Bringing the plagues upon the Egyptians was G‑d's way of causing this impure spiritual power to reflect back on those who brought it in the world, and deflect it away from the Jews.

Intellectual traits, though, are a different story. Pure intellect is not evil. A person with a good intellect may use it in a positive or negative way, but the intellect itself is not intrinsically evil. Therefore, the final three plagues – which correspond to the three intellectual powers with which G‑d endowed man – were not of materials or activities considered impure by the Torah.

The eighth plague was that of locusts, which are considered kosher by the Torah. The horror of the plague was in the quantity of locusts which descended upon Egypt. There were so many of them that they simply ate all that was in their path. The locusts themselves, though, were kosher.

The ninth plague – darkness – actually comes from a very high source. Every morning, we say the blessing over He Who has "formed light, and created darkness." "Creation" (beriya) is a higher spiritual level than "formation" (yetzira), and therefore in this blessing, darkness takes precedence over light. Blindness, for example is explained by the sages as the result of an overabundance of light; one who is blind is born without the ability to filter out enough light to see. The plague of Darkness then represents a blinding overabundance of light, as in one who receives a great intellectual illumination but does not know how to channel it in a usable direction. Perhaps even more illustrative, the ultimate source of fire (in Aristotelian physics, the "foundation" of fire) – is dark. Utter darkness, then, serves as the origin of illumination.

...this final plague came from the highest and purest spiritual source possible.

The tenth plague was killing of the first-born of the Egyptians. Although murder is, of course, forbidden by the Torah, justifiable forms of killing are not. In this case, it was G‑d Himself who killed the Egyptian firstborn either because of their cruelty to the Jews, or because they represented the highest power of intellect used in an evil way. Since the punishment was meted out by G‑d Himself, this final plague came from the highest and purest spiritual source possible.

Shem miShmuel explains that just as the first seven plagues eliminated the emotional power of evil in the Egyptians, so the final three plagues took out the intellectual power that the Egyptians had invested in evil and gave it to the Jews to be used positively – to receive the Torah and serve G‑d.

~~~~~~~~~~~~~~~~~~

[From "Inner Lights from Jerusalem" based on Shem miShmuel and other Chassidic and Kabalistic Sources, translated and presented by Rabbi David Sterne.]