The splitting of the Parshiot usually make, at least, some sense. However, in the next two Parshiot the plagues are split up (7 in the first, 3 in the second). Are there sources on why this may be? Is it teaching us something or was it done simply for time and length of parshas sake (I can't imagine this is the case, but maybe).
Abarbanel discusses this and gives two reasons why the parshiyos were split this way (which, incidentally, are the reasons @LarryK and @GershonGold have offered).
- The plague of arbeh was chosen to begin Parshas Bo with because it begins the makkos for which Pharaoh began to fear the plagues and negotiate with Moshe before the plague started.
- All the last three makkos took place in the dark. The locusts "darkened the land of Egypt" with their sheer mass. Choshech, clearly. Bechoros was at exactly midnight (although it would have been full moon, so it probably wasn't completely dark).
[Also, it makes the mnemonic work. First two letters of each parsha, Va'era and Bo add up in gematria to how many plagues are within.]
The seventh, Hail, marks a turning point. So it is also a good place to divide the parshiot.
The plague is a turning point since it is the first one whereby Moses/Gd gives Pharoh three choices:
- Let B'nei Israel leave
- Fully suffer the plague
- Partially suffer the plague: save your fieldworkers and animals by bringing them indoors away from the hail (Ex 9:19)
In prior plagues, only the first two choices were given. Sometimes the first choice was implicit.
But for the seventh, a clear choice on severity was provided to Pharoh. And note the response: those servants of Pharoh who feared Gd brought in their fieldworkers and animals from the fields. Those that did not directly enabled the death of their fieldworkers and animals by leaving them in the field. See Ex 9:20 - 21.
Drash: While some of Pharoh's servants recognized Gd and saved their people, Pharoh himself willfully sacrificed his field workers and animals in his denial of Gd. Pharoh felt no connection or concern for his field workers and animals. He was beyond redemption.
The seventh plague enables Pharoh to clearly show that he was not the "Gd" of his people. (For he would have saved them if that was so.) Rather, he was only concerned for himself and his dynasty. Thus the Parsha ends and sets the stage for the final surrender of Pharoh.
Source: Teachers of Pardes
I remember hearing that the 3 last Makos all had to do with darkness. Arbeh - grasshoppers covered the entire ground as it says וכסה את עין הארץ ולא יוכל לראות את הארץ, then you had Choshech - darkness where the Posuk says they were literally able to touch the darkness וימש חושך, and then Makas Bechoros which happened at midnight ויהי בחצי הלילה וה' הכה כל בכור.
The Baal HaTurim also mentions that when Hashem told Moshe Bo El Pahro, Bo = 3, and it was alluding to the fact that there will be three more Makos.