Exode 7:25

And seven days were completed after the Lord had smitten the river, and the Word of the Lord had afterward healed the river.

And seven days were fulfilled after that the Eternal had smitten the river. This is connected with the verse above, and the purport thereof is as follows: And with this (And it was fulfilled) seven days, using a singular verb when the verb actually required is a plural: vayimal’u (and they were fulfilled). Rashi explained it by adding the word minyan (number) in the singular, explaining it thus: “and the number of seven days was fulfilled.” Ramban suggests that the verse is connected to the preceding one and is to be understood with the additional word of bazeh (with this), thus rendering the sense of the verse: “and with this activity — i.e., with the Egyptians’ digging, etc., as stated in the above Verse 24 — was filled (or completed) seven days.” — namely, the Egyptians’ digging round about the river for they could not drink of the water of the river, [as stated in Verse 24] — with this was filled the seven days after the river had been smitten.

שבעת ימים, this was the duration of the plague that struck the river.

וימלא שבעת ימים, “seven complete days had passed.” According to Rashi, this was the pattern of all the plagues, that a plague lasted for one quarter of the month, whereas the warning that preceded it was in effect for the other three quarters of that month, so that each plague was relevant for a whole month. This interpretation is derived from Psalms 135,9: שלח אותות ומופתים בתוככי מצרים, “He sent signs and miracles against Egypt.” The last two letters in the word בתוככי, whose numerical value is 30 were unnecessary, and are the hint that each plague was relevant for 30 days.Our author raises the point that according to the wording in Rashi, the month had only 28 days then. He suggests as a possible solution, that the Egyptians were given the extra two days after the completion of each plague as a sort of “relief” before the warning of the following plague was issued. A further question is raised concerning the length of the plague of darkness, where the Torah described the most intense portion of that plague as having lasted for three days. (Exodus 10,22-23). He suggests that when we read in Exodus 14,20: ויהי הענן והחושך, “there was both the cloud and the darkness,” (as the beaches of the sea of reeds) the missing days were made up. (Compare Sh’mot Rabbah 14,3.) It is notable that in the Haggadah shel Pesssach, the text we read on the first night of Passover, where Rabbi Yehudah sums us the plagues on an acronym- דצ'ך עד'ש באח'ב, and everyone asks what he contributed to our understanding of those events by doing so, that Rabbi Yitzchok son of Rabbi Asher, who was born on the same calendar date as the death of his father, so that he was given the same name as that of his late father, they applied to him the words of the verse: וזרח השמש ובא השמש, “a new sun began to shine as soon as the sun had set,” (Kohelet 1,8) pointed out that when we place the three acronyms of Rabbi Yehudah one on top of the other like this: דצך, עדש, באחב you will find both at the beginning, the middle and the end the acronym for the three plagues of כנים, שחין, and חשך. [Our author adds that he will not elaborate further, presumably because he had not figured out how this is arrived at by Rabbi Yitzchok. This editor remembers his father of blessed memory explaining to him, that these were the three plagues not preceded by a warning. Ed.] Rabbi Yehudah may have wished to remind the reader that the order in which the plagues occurred was the one listed in the Torah, and not the order in which the plagues are listed in the Book of psalms (chapter 105). The Talmud in tractate Sanhedrin, folio 81 [Mishnah] relates that it was customary if people had been administered 39 lashes for having committed sins that qualified for such a penalty, if they sinned repeatedly, to lock them up and feed them a diet of barley until the sinner’s intestines collapsed and he died.