When is it forbidden to eat before Mincha?

From half an hour before alos hashachar, beginning a meal is forbidden. There is a concern that one may become involved in the meal and forget to daven. As of alos hashachar, any eating is forbidden-- since it is forbidden to eat from the time that davening is permitted until one davens. If one was unable to daven Shacharis, the prohibition against eating before davening is still in force; he may not eat anything from midday until he davens Mincha.  It is also forbidden to eat before laying tefillin.

סעיף ה, ס"ק כ, כג ו־כד, וביה"ל ד"ה היה עוסק וכו ביאורים ומוספים דרשו, 5

May one complete a task that he started before Kriyas Shema?

It is forbidden to begin any lengthy activity from alos hashachar until one has said Kriyas Shema and davened. There is a concern that a person might become so involved in the activity that he could forget to daven. Some say that one may not begin such an activity from a half-hour before alos. If a person started already, the question of whether he must stop depends on the following: 1) Regarding Kriyas Shema, which is a Torah obligation, one may complete an activity that he started at a permissible time as long as there is enough time to say Shema after he is done. If he started when it was forbidden to begin, he must immediately stop. 2) For tefilah, which is only mid’rabonon, one may finish what he is doing regardless of when he began the activity.

סעיף ה, ס"ק כג ו־כה, וביה"ל ד"ה היה עוסק וכו'; ביאורים ומוספים דרשו, 53-51

Is a public servant exempt from Shema?

A person who is involved in a mitzvah is exempt from performing another mitzvah, even if it means missing the second mitzvah entirely. Therefore, if one is involved in an important public service which cannot be done by someone else, he is exempt from Shema until he completes the task. He is also exempt if he needs to take a rest to strengthen himself for the job at hand. An important public service includes preventing someone’s money from being lost. Even if a person is being paid for his actions, he is exempt, as long as he was also intending to do a mitzvah. If he can interrupt himself to say Shema, he must do so.

סעיף ד, ס"ק יח-כ, שעה"צ ס"ק טו, וביה"ל ד"ה היה עוסק בצרכי; ביאורים ומוספים דרשו, 34 ;וראה שם, 4

• A woman is exempt from saying Kriyas Shema because it is a time-bound mitzvah. She should, however, be mekabel ol malchus shomayim daily by saying the pasuk of Shema Yisroel. Some poskim encourage women to say the entire Shema.

• The Rishonim disagree about whether there is an obligation of chinuch for the mitzvah of Kriyas Shema. Some say that there is not, since a child is not usually with his father during the nighttime and early morning hours that he recites Kriyas Shema.  Although the halacha follows the lenient opinion, one should try to be stringent.

• All opinions agree that there is an obligation of chinuch for the mitzvah of tefilah. For most mitzvos, chinuch begins when a child reaches the age of six or seven. Regarding tefilah, however, the poskim say that we should not take an exacting approach. A child is not expected to fully daven at that age; instead, the obligation only begins when he knows how to daven. 

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