Why does the Torah see fit to insert "Vehaysah lachem le'Chukas Olam"?
Seforno: Even when the Beis ha'Mikdash is standing and the Avodah is in effect, the Mitzvah of Shevisah from Melachah and that of fasting still apply. 1
To preclude from the notion that they come to replace the Avodah, and as long as the Avodah is in effect, they are not necessary.
Why does the Torah add the words "es Nafshoseichem"?
What does "Te'anu es Nafshoseichem" incorporate?
Ramban: Refer to 16:29:2:1.
Targum Yonasan: It incorporates eating and drinking, bathing, anointing oneself (with cosmetics), wearing shoes and desisting from intimacy. 1
Many Poskim rule that, apart from the prohibition against eating and drinking, all of these are only Asur mi'de'Rabbanan (See Na'ar Yonasan).
Why does the Torah write "ha'Ezrach"?