What is the connotation of "u'Shemartem Es ha'Matzos"?
Rashi #2 (citing Rebbi Yashiyah): By reading (not Matzos, but) Mitzvos, the Torah is teaching us not to let Mitzvos that come to hand become 'Chametz', but to perform them immediately.
Seforno: It is a Mitzvah to perform Mitzvos with Zerizus (swiftly and expediently), just as Hashem did with us. 3
Rashbam: It is an additional warning to eat Matzos on Pesach (night), to commemorate the exodus from Egypt. 4
In fact, in the event that one fails to do so (from the time of grinding and sifting), irrespective of whether the Matzos became Chametz or not, one has not fulfilled the Mitzvah of eating Matzah Shemurah, as the Gemara in Gitin (Rashi, in Chulin, 7a).
Through applying cold water should the dough show signs of rising (Rashi and Targum Yonasan), and through baking them swiftly, not giving the dough a chance to rise (Seforno).
As the Pasuk goes on to explain.
What is the connection between the Mitzvah to 'guard' the Matzos and the reason the Torah then gives for it?
Rashbam: Because Hashem took them out promptly when He did, the dough that they were preparing did not have time to rise. 3 Hence the Mitzvah to eat Matzah on the first night of Pesach to commemorate this. 4
What is the connotation of "u'Shmartem Es ha'Yom ha'Zeh"?
Rashi: It is an additional prohibition against performing work on Pesach. 1
Moshav Zekenim: It forbids Shevus (matters that Chachamim forbade on Shabbos); "ha'Zeh" excludes Chol ha'Mo'ed.
Otherwise, we would have thought that, since the Torah does not write 'Doros' or 'Chukas Olam' in connection with Melachah, the prohibition was confined to that year exclusively (Rashi).