Having mentioned the Mitzvah of keeping Shabbos at the beginning of the Parshah, why does the Torah repeat it here?
Rashi (citing Yevamos, 6a): To teach us that in spite of the Kavod of the Beis-ha'Mikdash (which the Pasuk is about to mention), its construction does not override Shabbos. 1
Ramban and Moshav Zekenim #1: The Torah is warns against Chilul Shabbos many times, because, like Avodah Zarah, it is equivalent to all the Mitzvos combined - and anybody who does not keep Shabbos it is as if he denies the fact that Hashem created the world, and has no Torah at all.
Seforno (in Pasuk 29): After warning against desecrating Yisrael's sanctity, the Torah issues commands to honor the days and the locations that are holy. 2
Ibn Ezra and Moshav Zekenim #2: It is placed near 3 "Seret la'Nefesh" (in Pasuk 28) to teach us that mourning does not apply on Shabbos. Likewise [fear of] the Mikdash is mentioned here to teach us that the Kohen Gadol and people of the Mikdash do not behave like other mourners.
Moshav Zekenim #3 and Ba'al ha'Turim: It is placed after "u'Mal'ah ha'Aretz Zimah", because the Yamm-Tovim are the worst times for Z'nus, 4 and Shabbos too, when people eat and drink, 5 and before "Al Tifnu el ha'Ovos" because the Ovos do not answer on Shabbos.
See Sifsei Chachamim and Torah Temimah, note 229. The Gemara there actually learns it from the words "Ani Hashem" - 'Kulchem Chayavim bi'Chevodi!'
Seforno: Hence "My Shabbasos" incorporates the Yamim-Tovim, and "My Mikdash", all holy places - such as Batei Midrash and Batei K'nesses - thereby accentuating the sanctity of time and space.
The Ibn Ezra explains that also "Al Techalel es Bitcha" (Pasuk 29) needs to be mentioned near Seret la'Nefesh, because wounding one's daughter over a Meis will lead to Z'nus. Others however, reject this explanation (Karnei Or).
See Kidushin 81a.
As the Navi writes in Hoshe'a 4:11 "Z'nus ve'Yayin ve'Sirosh Tikach Leiv." See also Ba'al ha'Turim on Pasuk29.
Why does the Torah write "Shabsosai" in the plural?
Seforno: To incorporate the Yamim=-Tovim (which are also called 'Shabbos).
What are the connotations of "Mikdashi Tira'u"?
Rashi (citing Yevamos, 6b): It is a Mitzvah to treat the Beis-ha'Mikdash with awe, 1 by not entering it with one's staff, wearing shoes or a money-belt, or without first washing one's feet.
Yevamos 6b: Comparing Mora Mikdash to Sh'miras Shabbos - just as by Shabbos it is not before Shabbos that one stands in awe but before the One who commanded it, so too, does one not stand in awe of the Mikdash 2 but of the One who issued the warning to do so.
Why does the Torah juxtapose Mora Mikdash to Shemiras Shabbos?
Yevamos, 6b #1: Refer to 19:30:2:2:
Yevamos, 6b #2: To teach us that, just as Sh'miras Shabbos is forever, 2 so too, is Mora Mikdash forevever - even after the Beis-Hamikdash is destroyed. 3
Oznayim la'Torah: Because both of them come to sanctify Yisrael, Shabbos in time and Mikdash in space. 4
