Exemptions TB Sukkah 25

Now that we have learned how to build a kosher sukkah, starting with daf TB Sukkah 25 we learn who is obligated to dwell within it. Ironically the first thing discussed are those people who are exempt from observing this mitzvah. “MISHNA: Those on the path to perform a mitzva are exempt from the mitzva of sukka. The ill and their caretakers are exempt from the mitzva of sukka. One may eat and drink in the framework of a casual meal outside the sukka.” Sefaria.org translation)

Rashi gives three examples of people who are exempt from observing the mitzvah of dwelling in a sukkah because they are involved in the observance of a different mitzvah (הָעוֹסֵק בְּמִצְוָה פָּטוּר מִן הַמִּצְוָה ). They are somebody who is going on a journey to study Torah, somebody who is going to greet his rebbe, and someone collecting funds to redeem captives. These people are not only exempt during the daytime while they are traveling, but also at night wherever they are staying.

Tosefot (ד"הּ שליחי מצוה) comment that the halakhic principle “one who is engaged in a mitzva is exempt from performing another mitzva” only applies when the person can't do both mitzvot by citing.an example from TB Nedarim 33b. A person finds a lost animal but does not have time to return it to the owner. He makes an oath that he will take care of the animal until he has the time to find the owner. If a poor person comes knocking on his door for tzeddakah, he can't ignore him and use the excuse of "I'm taking care of the lost animal" those hours he isn't caring for the animal. Obviously he can observe both mitzvot, providing for the poor and taking care of the animal. He may ignore the knocking on the door if he is actually involved in the care of the animal based on the principle. “one who is engaged in a mitzva is exempt from performing another mitzva.”

Of course, if a person can't do a mitzvah, it is obvious that he is exempt from observing it. What is the novel idea that tosefot is teaching? The Ritva explains the novel idea of the tosefot. Once a person is engaged in one mitzvah, it changes the status of the other mitzvah. It's no longer a mitzvah for that person, but rather it becomes not obligatory (רשות).

Not all rishonim agree with tosefot’s interpretation.