מועד לאמר, Moses announced the timing of the plague so that the Egyptians could not claim that the plague was a natural disaster.

פיח, ash, dust particles remaining at the bottom of the furnace light enough to be carried by the wind.

פורח, chemically active, producing spontaneous growth of bacteria.

מגפותי, different damage causing plagues, such as fire, hail, and brimstones, snow and heavy smoke.

כי עתה, at the time when I afflicted the livestock, I had actually considered also afflicting you personally with the same plague. I meant to wipe you out from earth. The only reason I did not do so as yet was בעבור הראותך את כחי, to show you My power and to convince you of the nonsense you uttered when you had said that you do not know of My existence (5,2).

NEVERTHELESS I HAVE SPARED YOU FOR THIS PURPOSE: IN ORDER TO SHOW YOU MY POWER, ETC. To inform you of your foolishness, in your saying (5:2), "I do not know Adonai.

מסתולל, the reflexive mode of the verb סלל as in סולו סולו דרך הרימו מכשול, “pave, pave a way and remove every obstacle, etc.,” (Isaiah 62,10). Just as the stones are pressed together to remove them as obstacles, so Pharaoh squeezed the Israelites so that they could not offer any resistance. Compare also Jeremiah 34,11 ויכבשום לעבדים ולשפחות, they “compressed” them into becoming male and female slaves. Concerning the grammatical principles underlying the use of the reflexive conjugation mitpael, every time this conjugation appears it has the letter ת preceding the first root letter, except the ones that have that letter at the end instead of at the beginning. Examples of the former are Psalms 94,4 יתאמרו כל פעלי און Words such as יתברך, יתגדל or in Ezekiel 38,23 והתגדלתי והתקדשתי, or Jeremiah 9,23 יתהלל המתהלל, or מתפלל in Exodus 10,2. The author lists a few more examples, showing that all of the letters of the aleph bet except the 7 letters ד'זט ס'ץ ש'ת, follow this pattern. When the first root letter is either a ש or a ת, the letter ת is appended at the end instead of at the beginning. The exception is a word whose root begins with the letter ס. One such example is our verse, the root being סל. The basic meaning is parallel to Numbers 16,13 תסתרר עלינו, where the word תסתורר is derived from the root שר. In examples such as ישתבח, ישתמר or משתכר, all of which have roots beginning with the letter ש, the letter ת signaling the conjugation התפעל is deferred until after the first root letter. In roots commencing with the letter ז or צ, no such letter ת signaling the reflexive conjugation appears at all. Instead, after the letter צ the letter ט is added to show us that we deal with the reflexive conjugation. Well known examples of these constructions are found in Genesis 44,16 נצטדק from the root צדק, and Joshua 9,12 הצטיידנו from the root ציד, provisions. Concerning the words with the first root letter ז, the letter signaling the reflexive conjugation is a ד, as in Daniel 2,9 הזדמנתון. The letters ד-ט-ת, by themselves when they appear at the beginning of the word, do not get an additional letter to indicate that the construction in which they appear is a reflexive conjugation. A prominent example of this is Numbers 7,89 וישמע את הקול מדבר, where the Torah did not write מתדבר. Another such example is Leviticus 21,4 לא יטמא בעל בעמיו, where because the root טמא begins with the letter ט the Torah did not write יתטמא, although the verb is in the reflexive mode, of course. The same is true in Samuel II 22,27 where the word תתפל in the line ועם עקש תתפל, does not have another letter ת at the beginning in order to signal that the verb is in the reflexive mode. [The author illustrated his point with still more examples, but I think he made his point adequately with the examples I have cited. Ed.]

העז, “gather in!” (as a form of escaping the hail) We find this word in a similar sense in Jeremiah 6,1העיזו אנשי בנימין!, “flee for refuge O people of Binyamin!” A similar verse in Isaiah 10,31 reads יושבי הגבים העיזו, “the dwellers of Gevim sought refuge.”

חטאתי הפעם, now, this time I admit that I have sinned.

כי טרם תיראון, as per Onkelos: “you have still not acquired an awe and reverence for Hashem.”

לא נוכו, to inform us that whatever the hail had not destroyed would be destroyed by the locusts. The hail demolished everything hard, the locust everything soft.

נתך, an expression similar to יציקה, “pouring.” We find this root on this sense in Ezekiel 22,22 כהתך כסף בתוך כור כן תותכו בתוכה, “as silver is melted (poured into for refining) in a crucible, so you shall be melted in it.”

ויוסף לחטוא, up until now he had not been a deliberate sinner, not having acknowledged that what he had been doing had been sinful. Now, after having acknowledged this, reneging constituted a deliberately committed sin. This is why the Torah now describes Pharaoh as a deliberate sinner.