What is the definition of "Bein ha'Arbayim", and why is it called by that name?
Since when is Pesach on the 14th of Nisan?
Rashi: Pesach in this Pasuk refers (not to the Yom-Tov, but) to the bringing of the Korban by the same name.
Since the fourteenth of Nisan is not included in the Mikra'ei Kodesh, why does the Torah insert it here
Seforno: Because it is the cause of the fixture of the Yamim-Tovim, 1 since, on account of the first Korban Pesach that was brought in Egypt, Pesach must always be arranged to fall in the spring - like it did then. 2
Oznayim la'Torah: I fact, it is the main reason for fixing a leap-year ? as the Torah writes in R'ei, Devarim, 10:1 "Shamor Es Chodesh Ha'aviv". Se Oznayim la'Torah.
Seforno: As the Torah indicates in Devarim 16:1.
Why does the Torah write "Pesach la'Hashem"?
Moshav Zekenim, citing R. Eliezer of Garmaiza: It is a time when Hashem has mercy on his creations, from the Creation until now. Refer to Sh'mos 12:11:4:2.
Moshav Zekenim #1: "Peh Sach" - [Avraham's] mouth, which said "ba'Meh Eda", caused His children to be enslaved until this time.
Moshav Zekenim: "Pesach" is the acronym of 'Peh Sach', as if to say The mouth on the Merkavah (Hashem's chariot) speaks ? It announces that the time to redeem Yisrael has arrived. In other words, the letters on the Merkavah advocate for Yisrael.