The Torah relates that Moshe and Aharon came to Pharaoh. What happened to the elders?
Rashi: The elders slipped away (out of fear) one by one, so that, by the time Moshe and Aharon reached the palace, they had all disappeared. 1
Rashi: That explains why, at Matan Torah, Hashem said that they were not to approach Har Sinai - Midah Keneged Midah. (Most explain Rashi to say that they did not approach more than the Am, unlike Ramban (24:10) and Moshav Zekenim (24:1). Divrei David says that they came close to bow, but needed to go back, and so it connotes below (24:9,14). - PF)
Why did Hashem go to the trouble of warning Pharaoh? Why did He not simply destroy the Egyptians (for what they had done to Yisrael)?
Rashi (in Devarim): As Moshe explained (upon sending a message of peace to Sichon), he took his cue from Hashem, who could just as well have sent a bolt of lightning and wiped out the Egyptians; yet He sent him (Moshe) from the desert to ask Pharaoh - nicely to let His people go. 1
Seeing as Hashem planned to take Yisrael out of Egypt, why did he instruct Moshe to only ask for permission for Yisrael to sacrifice in the desert?
Refer to 3:18:2:1,2.
Because the earliest time for the termination of the Galus would only fall due in the following year. Meanwhile, He wanted Pharaoh to acknowledge Hashem's Omnipotence, and that Yisrael were His people.
Why does the Torah omit the phrase "v'Ne'elam Mimenu", that appears in the cases that follow?
Rashi (Shabbos, 68b) and Ramban: Because in this particular case, he is subject to a Korban even be'Meizid. 1
Ramban, Moshav Zekenim: Or b'Shogeg about the Isur to swear falsely, if he remembered the testimony. However, if he forgot the testimony he is exempt.
Rashi writes that the elders slipped away, and therefore at Matan Torah, they were not allowed to come close. Aharon came with Moshe, but also he could not come as close as Moshe!
Riva, Moshav Zekenim: Moshe is mentioned before Aharon, for Aharon did not invigorate himself for the Mitzvah [to come to Pharaoh] as much as Moshe did.
Why is there a Vov in "Lo"?
Moshav Zekenim: We read "Lo" like with a Vov - if he testified for him, he cannot return and testify again [differently].