Literary Devices – Shemot 7

The roots "כבד" and "חזק" appear only a couple of times in the chapter, but might be key words throughout the narrative of the Exodus.

• Concordance – Tracing the usage of both the verb and adjective "כבד" in Torah¹ reveals how they appear throughout the Exodus narrative,  from the initial "heavy" famine that causes the nation to descend to Egypt to the "great" wealth with which the nation leaves Egypt.² Similarly, both the adjective and verbal root "חזק" repeat in the narrative, referring on one hand to Paroh's obstinance in preventing the Exodus and on the other to God's mighty hand which brings it about.

• See Prof. Yonatan Grossman's Leitwort for general discussion of the phenomenon of keywords, mentioning the role of the root "כבד", and R. Nathaniel Helfgot's שתי מילים מנחות בסיפור יציאת מצרים, who explores the usages of the two roots כבד and חזק.  Both authors note how the repetition of the roots demonstrates Hashem's measure for measure actions during the Exodus.³

• שרץ – The description of the frog's proliferation using the somewhat rare root "שרץ" (swarm) recalls both the swarming in the stories of Creation and Recreation post Flood and the description of the population growth of the Children of Israel in Shemot 1:7. [See the concordance that over half of the root's appearances occur in these stories.] 
• באש – See the concordance that this root, as well, is somewhat rare. It is used here (Shemot 7:18, 21) to describe the foul smell let off by the dying fish, and recalls Shemot 5:21, when the Israelites worried that Moshe’s advocacy would sour their reputation with Paroh: "הִבְאַשְׁתֶּם אֶת רֵיחֵנוּ בְּעֵינֵי פַרְעֹה". 

• See Bereshit Rabbah that the "שרץ" allusion is meant to remind all that it is God, not Paroh, who is the Creator.  Just as He originally had life swarm, now He has frogs multiply, but this time – to undo creation.⁴
• Both allusions might alternatively be meant to hint to a measure for measure punishment. See the Mekhilta DeRabbi Yishmael, Tanchuma, Eliyahu Rabbah and others who view the plagues in this manner.⁵ The Egyptians' revulsion at the nation's proliferation is punished with the revolting plague of multiplying frogs.⁶ Paroh’s viewing of the nation as befouled is punished by the NIle's reeking.

• See Purpose of the Plagues for discussion of various approaches to the choice of plagues including both the idea that they were an undoing of creation with an educative goal, and that they were measure for measure punishments.
• .See Z. Zevit, "Three Ways to Look at the Ten Plagues: Were They Natural Disasters, a Demonstration of the Impotence of the Egyptian Gods, or an Undoing of Creation?" BR 6 (1990): 16-23, who suggests that the ten  plagues were chosen specifically because they corresponded to aspects of the word's creation and could thereby teach both the nation and Egypt that Hashem is the Creator.
• See Darkness Deciphered, by Shira Smiles, for an analysis of the plagues as a reversal of creation.
• See “All Are Considered Blind”, by R. Aaron Lopiansky, for analysis of the purpose of the plagues as a reversal of creation, with an emphasis on the plague of darkness and the religious message of the plagues.
• See The Microcosm Manifest in the Makkot, by Aryeh Krischer, for analysis of the order of the plagues in relation to the order of creation.

Blood is an important symbol in the story of the Exodus, related to both punishment and covenant / redemption. 

• Blood appears twice in Chapter 4, first in the context of the miracle of turning water to blood and then in the story of the circumcision of Moshe’s son. 
• In Shemot 7, the plagues begin with blood.
• The exodus itself is connected to the blood of the Passover offering that the Israelites smear on their doorposts.
• The alternating symbols of blood as punitive plague aimed at ending the Egyptian bondage and blood as symbol of the covenant (both circumcision and the Paschal sacrifice) hint to the underlying theme of the Exodus as representing the transition from being slaves of Paroh to being servants of Hashem.

Water is also a recurring symbol in the story of the exodus, representing the confrontation between the lifegiving force of the Nile (representing Egyptian culture and power) and the Source of all life, Hashem.