Why did Moshe discuss the Mitzvah of Shemiras Shabbos before the Meleches ha'Mishkan?
Rashi, Ramban and Seforno: To teach us that building the Mishkan does not override Shabbos. 1
Because the sanctity of time is greater than that of location. See also Ba'al ha'Turim.
Why does the Torah write "Te'aseh Melachah" and not Ta'aseh Melachah"?
Oznayim la'Torah: Because it is not an individual Mitzvah to work during the week but a collective one to ensure that work is done during the week exclusively, but not on Shabbos. 1
Moshav Zekenim: To teach us that, when Yisrael are meritorious, their work is done by others.
Having already taught us (in Ki Sisa, Sh'mos, 31:14) that Chilul Shabbos is subject to the death-penalty, why does the need to repeat it here?
Seforno: To teach us that one is Chayav Misah even though he was performing a Mitzvah.
Mechilta: Because we would otherwise have thought that when Hashem said "Ve'asu Li Mikdash", He meant even on Shabbos. 1
Torah Temimah: Seeing as, once it has been built, bringing the Korbanos does override Shabbos. Or because now that we have access to Kedushas ha'Makom during the entire week, Kedushas ha'Zeman only once a week is no longer necessary (Oznayim la'Torah). This is not correct however, since Shabbos applies even where there is no Beis-Hamikdash and even when it is not standing (Oznayim la'Torah).
What are the implications of the word "Yih'yeh lachem Kodesh"?
Mechilta: It implies that it is holy for you (for your private affairs) but mundane for (matters that concern) Hashem - Korbanos, which may be brought on Shabbos. 1
See Torah Temimah, note 4.
Why does the Torah here write here "Kodesh "Shabbos Shabason", and in Beshalach 16:23) "Shabason Shabbos Kodesh"?
Moshav Zekenim (in 16:23): To teach us that one must add from Chol on to Kodesh. (refrain from Melachah) both before the actual Kodesh, and after the Kodesh (on Motza'ei Shabbos).
QUESTIONS ON RASHI
Rashi writes that here the Torah teaches that building the Mishkan does not override Shabbos. Why is this necessary, seeing as Shabbos is an Asei and a Lo Sa'aseh, and the Gemara states in Bava Metzi'a 30a that an Asei does not override an Asei and Lo Sa'aseh?
Tosfos (in Yevamos 6a DH 'Nigamer'): Because (whereas normally an Asei does not override an Asei and Lo Sa'aseh, since one Asei is not stronger than another), building the Mikdash is stronger than the Asei of Shabbos, due to fear of the Mikdash.
Ritva (in Yevamos 6a, citing R. Yonah): The Asei of Shabbos applies only to Av Melachos that are stringent. 1
Torah Temimah: Refer to 35:2:2:2*.
One might have thought that Binyan ha'Mishkan overrides Toldos, or making animals work... (PF)
Rashi writes that here the Torah teaches that building the Mishkan does not override Shabbos. We already know this from (Vayikra 19:30) "Es Shabsosai Tishmoru u'Makdishi Tira'u" (Yevamos 6a)!
Moshav Zekenim: The current Pasuk teaches us that all the Melachos used to construct the Mishkan are forbidden on Shabbos.
