As you heard it from Me. . . Rashi is explaining why it says, “All that I command you.” You (Moshe) will say each statement before Pharaoh, concisely and only once, just as you heard it from Me. And Aharon your brother will express each statement a few times, eloquently, until it is palatable to the ears of Pharaoh. (Maharshal)

And in opposition towards Me. . . Rashi is answering the question: Pharaoh will surely defy Hashem if He hardens his heart. Is this Hashem’s way, to induce a person to transgress His will? Therefore Rashi explains, “And it is revealed to Me. . .”

It is better for Me that his heart be hardened. . . In other words, if I do not harden Pharaoh’s heart he will surely repent. But it is revealed to Me that he will not really repent wholeheartedly. And then, if I smite him with plagues and punish him, people will say that Hashem brings punishment upon repenters — for they will not know that Pharaoh’s repentance was not wholehearted. Therefore I will harden his heart so that he will not repent at all, and then I will be able to increase My wonders and punish him for all to see.

And you will thereby recognize My power. . . Rashi inferred this because it is written, “to increase My signs,” implying that Hashem will punish Pharaoh more severly in proportion ot his sins. This raises a difficulty: Why should Hashem want to bring more plagues on Pharaoh than he deserves? Thus Rashi explains: In order that “you will thereby recognize My power.” And Rashi then brings a proof for this concept: “This is the way of Hashem. . .”

Nevertheless, concerning the first five plagues it does not say. . . Rashi is saying that even though Hashem should have strengthened Pharaoh’s heart in the first five plagues as well, [He refrained from doing so] because He wished to publicize Pharaoh’s wickedness — so that people should know that even without Hashem strengthening his heart, he strengthens it on his own. Therefore, Hashem did not do so until after the first five plagues.

A sign. Since Rashi interprets מופתים as “wondrous plagues,” in Parshas Va’es’chanan (Devarim 4:34), he needed to explain that here מופת means “a sign.”

To make it known that there is power. . . [ צרוך means power], i.e., the One Who sends you has power and rulership, as it is written in Parshas Ha’azinu (Devarim 32:17), “They will sacrifice to demons that have no power,” and Onkelos there translates as, “. . .that have no צרוך .”

A serpent. The term תנין when on land means a serpent (i.e., a snake). And when in the sea it means a [kind of] fish. So too does the Radak explain תנין .

For it appears to rotate by magic. In other words, this sword rotates on its own, and a person who sees it thinks it rotates by magic. Accordingly, the word להט which appears there connotes “magic.”

After it became a rod again did it swallow all the rest. I.e., since it is not written that “Aharon’s serpent swallowed,” we infer that “after it became a rod. . .” If it was still a serpent when it swallowed the others, it would be only one miracle. But [this occurred] after they [all] became rods again, as it is also written “[Aharon’s rod swallowed] their rods,” so it was a double miracle. (Re’m)

Which I will begin with the word כה**. . .**Regarding the other plagues, כה is written at the warning, but not at the actual plague. Whereas for the killing of the first-born, כה אמר ה' is written at the actual plague.

The water in the wooden vessels and the stone vessels. Rashi is explaining that the plague affected only the water in the vessels, but not the wood and stone vessels themselves.

בלטיהם refers to works of demons. . . This is because demons walk בלט (with stealth). In Sanhedrin 67b it says: R. Aiba bar Nagari said in the name of R. Chiya bar Abba, בלטיהם is works of demons; בלהטיהם is witchcraft. And so it says (Bereishis 3:24), “The להט of the sword. . .” Rashi (Sanhedrin, ibid.) explains בלטיהן as in (Shoftim 4:21): “And she went to him בלאט (with stealth).”

The number of seven days. . . Rashi is explaining why it is not written וְיִמָּלְאוּ , [the plural form of “full,” instead of וימלא , which is the singular form.] Rashi explains that וַיִמָּלֵא refers to the number, [which is singular,] and not to “seven days.”

For each plague functioned for a quarter of a month. . . in other words, seven days. You might object: But the plague of darkness lasted only six days, as indicated in Parshas Bo (10:22). The answer is: Later, in Parshas Beshalach (14:20) it said: “There was cloud and darkness and the night was illuminated.” This means: The cloud and darkness was for Egypt, while the night was illuminated for Yisrael. And why was there darkness for Egypt? Because there, Hashem punished them with the seventh day of darkness that He did not bring upon them at first.

It is describing a person based on an ongoing action. . . [Rashi is answering the question:] מָאֵן implies that Pharaoh constantly refuses. And that is not so, for just because Pharaoh refuses now, therefore will he constantly refuse? Thus Rashi explains: “It is describing. . .” [And to prove the point,] Rashi says it is similar to שלו ושקט , which [due to their grammatical form] imply a permanent, ongoing condition, yet [in fact they only] describe a temporary condition, [since no one is constantly serene and at ease]. Similarly with סר וזעף , which imply permanency although they are only temporary. Therefore Rashi explains, “It is describing. . .”

They would enter and croak. מקרקרין means crying out and making noise.