What is the corrolary between "Mos Yumas" and "ve'Nichr'sah ... "?
Rashi: "Mos Yumas" if there were witnesses and warning; "ve'Nichr'sah", if there were not. 1
Seforno: They are actually two additional reasons as to why building the Mishkan does not override Shabbos: 1. Because Shabbos incorpoates an Asei (Ki Kodesh Hi lachem") and a Lo Sa'aseh ("Mechalelehah Mos Yumas"); 2. Because desecrating is an excptionally severe sin inasmuch as the soul of the sinner is cut off from the world to come. 2
Ramban: "ve'Nichr'sah ha'Nefesh ha'Hi me'Amehah" means that, after the Mechalel Shabbos dies, his Soul will not return to the vicinity of Hashem, where the other souls go after death. 3
Why is the punishment for transgressing Shabbos so severe?
Seforno: Because someone who breaks Shabbos denies the Creation, and he therefore has no portion in the Mishkan or in the One who dwells in it.