Why does the Torah begin with "ba'Chodesh ha'Shelishi" and only later insert "Vayis'u me'Refidim" (as it did earlier - See 16a [Ramban])?
Ramban: Because the Torah wants to stress the great joy that they felt at arriving at Midbar Sinai, which they had eagerly awaited from the moment they left Egypt. 1
Moshav Zekenim (Sof Perek 18): The Torah put "ba'Chodesh ha'Shelishi" next to Yisro's departure to teach about waiting three months afraid freedom before marrying. Refer to 19:1:151:1.
To which day does "Yom ha'Zeh" refer?
Why does it write "ba'Yom ha'Zeh" and not "ba'Yom ha'Hu"?
Rashi: To hint that the words of Torah should be fresh in our minds, as if they had been given to us on that day. 1
Moshav Zekenim: On this day was fulfilled (3:12) "Ta'avdun
Moshav Zekenim: We learn this primarily from "ba'Chodesh" (this is like 'Chadash').
Why was Matan Torah in the third month?
Rosh, Hadar Zekenim #1: A [female] convert, captive or freed slave must wait three months 1 before marrying 2 or becoming betrothed. All three of these applied to Yisrael. (Matan Torah was like Yisrael's marriage 3 to Hashem
Rosh: Hashem should have waited three full months. Amidst dearness [of Yisrael to Hashem], He gave the Torah on the sixth of the third month. (If we count from leaving Egypt, it was less than two full months! Perhaps the Rosh counts from Rosh Chodesh Nisan, when the first Mitzvah was given to Yisrael. - PF)
This is an Asmachta. Chachamim decreed so to avoid Sefekos of lineage. Any child born more than six months after the three month wait was conceived in Kedushah from the new husband. Any child born within six months is is not from the new husband. (However, if a captive gave birth within nine months of being captured, it is a Safek if the child is from her husband or the captor. - PF)
Moshav Zekenim: Everything about Matan Torah was like a marriage. Moshe took out Yisrael, like they take the Chasan to the Kalah. The clouds of glory were the Chupah. Moshe and Aharon were the Shushbinim (close friends). The Luchos were the Kesuvah. We give to a virgin Kalah 12 months to prepare for Chupah
Why was the Torah given in the Midbar, and not in Eretz Yisrael?
Moshav Zekenim 1 #1, Pane'ach Raza: It is lest the nations have a complaint 'why did You not give Torah to us?!'
Moshav Zekenim #2: Torah is Hefker for anyone [to acquire. It is not an inheritance. 2
Moshav Zekenim #3: It is lest everyone engage in his field, and Torah will be Batel. In the Midbar, everyone was free [to engage in Torah]. Chachamim said, Torah was given only to those who eat Manna (Mechilta).