Bearing in mind that in Shemos (7:2) Hashem instructed Moshe "Atah (you, singular) Tedaber", why did Hashem say here "Dabru" (plural)?
Rashi: Moshe and Aharon showed honor to each other. Each said 'teach me!", and the words came out from between them 1 as if they had both said them.
See Sifsei Chachamim.
Why did Hashem give instructions to take the lambs on the tenth - four days prior to the bringing of the Korban Pesach?
Da'as Zekeinim mi'Ba'alei Tosfos citing Rashi: To give them four days to busy themselves with the Mitzvos of (the blood of the) B'ris Milah and the blood of the Pesach. 1
Why did Hashem add the word "ha'Zeh"?
Rashi and Targum Yonasan: To teach us that it was only Pesach Egypt that had to be taken (designated) on the tenth, but not future Pesachim.
Mizrachi: Indeed, even future Pesachim must be checked for blemishes four days before Shechitah - but one may check several animals in advance, and designate his Pesach just before Shechitah.
Why was specifically a Seh (lamb or kid-goat) chosen as the Korban Pesach?
Ramban: It is based on the fact that Tleh (lamb) is the Mazal of Nisan. Consequently, Shechitah of a lamb demonstrated a. that we left Egypt (not on the strength of the Mazal, but) by the Grace of Hashem, and b. that Hashem humiliated the god that the Egyptians worshipped 1 , precisely when the Mazal that it represented was at its highest point (in the middle of Nisan). 2
Moshav Zekenim (verse 29) #1: Mazal Gedi (kid) begins to serve from midnight in Nisan; Tleh begins serving at the beginning of the morning. 3
Moshav Zekenim #2: Yisrael of that generation transgressed Arayos and idolatry. The Seh atoned for "Seh Fezurah Yisrael" (Yirmeyah 50:17).
As the Midrash says 'Take for yourselves a lamb and slaughter the gods of the Egyptians' (Ramban).
These two points signify the first two Mitzvos of the Aseres ha'Dibros - Anochi and Lo Yihyeh Lecha.
I.e. Seh incorporates the ruling Mazalos at the time of Makah Bechoros (at which point Pharaoh insisted that we leave), and at the time we actually left. (PF)
Why the double expression "Seh l'Veis Avos, Seh la'Bayis"?