Having mentioned the Mitzvah of keeping Shabbos at the beginning of the Parshah, why does the Pasuk repeat it here?
Rashi and Ramban #2 (citing Yevamo, 6a): To teach us that in spite of the Kavod of the Beis-ha'Mikdash (which the Pasuk is about to mention), one may not construct it on Shabbos. 1
Ramban #1: The Torah 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 (on Pasuk 29): After warning against desecrating Yisrael's sanctity, the Torah issues commands to honor the days, the locations and the people that are holy. 2
What are the connotations of "Mikdashi Tira'u"?
Rashi: It is a Mitzvah to treat the Beis-ha'Mikdash with awe, by not entering it with one's staff, wearing shoes or a money-belt, or without first washing one's feet.