The Ramban understands that there are two independent mitzvos with challah. One is to separate challah, as it statesראשית עריסותיכם חלה תרימו תרומה the first of your doughs raise up a terumah. This separation removes the issur tevel, making the rest of the dough fitting to eat. The other mitzvah is giving challah to the Kohen, as it states מראשית עריסותיכם תתנו לה’ תרומה from the first of your dough’s give terumah for Hashem, which is given to the Kohen. The Rambam and Sefer HaChinuch disagree, stating there is one mitzvah with two parts: a person is commanded to separate challah from the dough and give it to the Kohen. Since the purpose of separating the challah is in order to give it to the Kohen, it is counted as one mitzvah.
The brachah on challah is ברוך… להפריש חלה מן העיסה. The Avudraham brings that the wordלהפריש is taken from Onkelos’ translation of the words תרימו תרומה, תפרשון אפרשותא you shall separate a separation, which defines the mitzvah of challah. So too the passuk states in regards to terumah, תרימו, which Onkelos translates תפרשון you shall separate it, and is the nusach of the brachah on separating terumah. The Avudraham explains that there is a brachah on separating challah, but not on giving challah or other presents of Kehuna, because they are zocheh to it from Hashem, as it states תתנו לה’. Everything belongs to Hashem and He gave the Kohanim 24 presents of Kehunah. The owner only decides which Kohen he favors to give it to.
The Sefer HaChinuch explains that a person’s life is dependent on food, bread being the main sustenance of a person. Hashem wanted to enable us to constantly merit the mitzvah of challah in order to bring brachah and zechus to ourselves. Bread is sustenance for the body, by eating it, and also a sustenance for the soul, by performing the mitzvah of challah. The Chinuch offers another reason: the mitzvah of challah was given in order to provide immediate and effortless sustenance for the Kohanim. Unlike the present of teruma, which are kernels of wheat that needs to be processed, sieved, grinded, kneaded, baked and only then eaten, challah is given prepared and ready for the Kohen to eat. This will provide him with the ability to be completely dedicated to the avodah in the Beis HaMikdash, and serve Hashem without the disturbance of working to make a living.
The Beraishis Rabbah brings: Chavah caused the challah of the world to be lost. This refers to Adam HaRishon who was separated as challah. She gave Adam to eat from the eitz hada’as, and he was sent out of Gan Eiden. Rashi explains that Hashem created Adam HaRishon as a baker kneads dough; first he puts the water into the flour, and afterwards he kneads the dough. So too Hashem caused it to rain and saturate the dirt, and afterwards He took the moist dirt and created Adam. The Machatzis HaShekel explains that just as dough is made fitting to eat after challah is separated, so too the world was fitting to function only after people were created since the entire purpose of creation is for Adam.
The Machatzis HaShekel adds that since Adam was created on Friday and the aveirah was done on Friday therefore women should separate challah on Friday, as an atonement. The Haga’os Maimoni brings that women are involved with chores done in the house, therefore they are specifically given this mitzvah to fulfill. He adds that a woman should daven when she separates challah that as a zechus from the mitzvah she should merit to have sons who are tzaddikim and yarei Shamayim.
May the zechus of the mitzvah of challah bring tikkun to the entire world, and help us have sons who are tzaddikim and yarei Shamayim!