At the beginning of this week’s parshah the Torah writes extensively about Avraham Avinu’s act of hachnasas orchim for the three men who were passing by his tent. Several Achronim are bothered by this action for the following reason: The first pasuk in the parshah says, “Vayeira eilav Hashem – And Hashem appeared to [Avraham].” The Gemara in Baba Metzia 86b says that Hashem had come to visit Avraham in fulfillment of the mitzvah of bikur cholim, as it was the third day after Avraham’s bris milah and he was considered sick. The presence of Hashem, however, did not stop Avraham from performing the mitzvah of hachnasas orchim. The Gemara in Shabbos 127 says that we learn from this that the mitzvah of hachnasas orchim is greater than kabalas p’nei haShechinah.
Achronim ask that since Avraham was in the middle of performing the mitzvah of kabalas p’nei haShechinah, why did he stop and start another mitzvah – hachnasas orchim? The rule is osek b’mitzvah patur min ha’mitzvah (while one performs one mitzvah he is exempt from another). The question is even stronger according to the opinion of the Ritva in Sukkah 25 that one who is performing one mitzvah is not allowed to perform another mitzvah.
The Nesivos Hamishpat (72:19) says that the general rule of osek b’mitzvah patur min ha’mitzvah only applies in a scenario in which one was performing an obligatory mitzvah. When one is involved in performing a non-obligatory mitzvah, he may perform another mitzvah if he wishes – even according to the Ritva. Therefore, if one is involved in a voluntary mitzvah and a poor man approaches him, he will be obligated to give him tzedakah.
Based on the opinion of the Nesivos, we can answer the question that was posed regarding Avraham Avinu’s engagement in the act of hachnasas orchim. Since the mitzvah that Avraham was performing (kabalas p’nei haShechinah) was not obligatory, he was allowed to engage in another mitzvah. The reason that Avraham chose to engage in the mitzvah of hachnasas orchim over the mitzvah of kabalas p’nei haShechinah presumably is because it is greater, as the aforementioned Gemara in Shabbos stated.
However, many Achronim were bothered by the ruling of the Nesivos. They state that the Gemara in Sukkah 26a says that individuals who sell tefillin are exempt from all other mitzvos. Selling tefillin is not an obligatory mitzvah, and yet the Gemara extends the rule of osek b’mitzvah patur min ha’mitzvah to those individuals. This seems to be a direct contradiction to the ruling of the Nesivos.
Perhaps we can suggest that the Nesivos agrees that even when one is involved in a voluntary mitzvah, the rule of osek b’mitzvah patur min ha’mitzvah will apply, as is evident from the Gemara in Sukkah. However, the exemption differs when one is performing an obligatory mitzvah as opposed to a voluntary mitzvah. When one is involved in performing an obligatory mitzvah, all other mitzvos are considered as if they are davar rishus (not mitzvos) for him; therefore he is exempt from performing them. There is even a discussion as to whether he would make a berachah on another mitzvah, since it is not considered a mitzvah for him.
When one is involved in a voluntary mitzvah, he is exempt from engaging in other mitzvos. However, we do not render all other mitzvos as if they were not mitzvos. It is merely a right to continue performing the mitzvah that he had started earlier. If one was involved with performing a voluntary mitzvah and decided to engage in another mitzvah, all would agree that he should make a berachah on the new mitzvah since it is a mitzvah even for him.