Why did Moshe place the Mitzvah of Shemiras Shabbos before Meleches ha'Mishkan?
Rashi, Ramban and Seforno: To teach them 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.
Having taught in Shemos (31:14) that Chilul Shabbos is subject to the death-penalty, why does the Torah see fit to repeat it here?
Seforno: To teach us that he is Chayav Misah even though he was busy with a Mitzvah.