Rabbi Shimon ben Lakish said, “Mitzvahs should not be passed over.”

What does this principle mean and what is its source? Rashi explains here on our daf that it means that once a mitzvah “comes to one’s hand” (i.e. presents itself), one should not bypass it or delay it. However, from the word m’achar in Rashi’s commentary, there seems room to ponder whether Rashi is merely making a statement to explain the words or if he is also giving the reason for this principle. If me’achar means “once” — i.e. “Do not pass over a mitzvah once it comes to your hand” — this is a statement but not a reason. But, if m’achar means “since” — i.e. “Do not pass over a mitzvah since it came to your hand — this would indicate a reason for not passing over it. “Since” and “because” it is in front of you to do, it would be a disgrace to the mitzvah to pass over it or delay it.

This same teaching of Reish Lakish of “Mitzvahs should not be passed over” is taught in other places in Shas as well. For example, it appears in Yoma 33a. There, Rashi clearly offers a reason for this important Torah principle, a teaching that is found in the Mechilta: The Torah states, U'shmartem et ha'matzahs —"And guard the matzahs" — which can also be read as “And guard the mitzvahs.” This means that if a mitzvah presents itself to a person, he should guard it and do it immediately, not waiting until it becomes “like chametz and old.” Accordingly, Rashi here is also using the word m’achar in the sense of “since,” and as being the reason behind the halacha.

There is also a deeper, spiritual idea behind this Torah principle of not delaying the performance of a mitzvah. Rabbi Akiva Tatz has explained it in the following manner: Just as matzah becomes chametz if left too long, so too a mitzvah, which is spiritual life for one who performs it, becomes chametz, fermented, sour, if it is allowed to become part of the natural. A mitzvah is a physical action containing unbounded spiritual energy, but if it is performed as no more than a physical action, it may lose its connection with the spiritual world. Mitzvahs are like matzahs. When performed with zeal and alacrity, they are transcendent, but when performed sluggishly, they sour.

Returning to Reish Lakish’s statement in the gemara: What is the context? The mishna teaches the order of the numerous steps involved in bringing the Pesach sacrifice in the Beit Hamikdash. After the shechita, the blood is received by a kohen in a bowl (bazich) of silver or gold, which is then passed from kohen to kohen until it arrives to a kohen who is near the Altar, who sprinkles its blood there. One halacha in the mishna is that a kohen should receive the full bowl from the previous person, on its way to the Altar, before he returns the empty bowl, on its way back from the Altar. Why does he receive the full bowl before returning the empty one? The gemara says that this supports the statement of Reish Lakish. Since the full bowl is being received and passed on to fulfill a mitzvah, it takes precedence over the empty bowl.

It is important to note that there are can be an exception to this rule, if warranted by the halacha. Normally the tefillin of the arm should be put on before the tefillin for the head. Why? The Torah says that the head tefillin will be v’hayu. Chazal (Menachot 36a) explain that this word teaches that when the head tefillin are on, the arm tefillin need to already be on (v’hayu is plural – Rashi). What should one who is putting on tefillin do if he mistakenly takes out the tefillin for the head first? Should he pass over it, putting it aside until first wrapping the tefillin for the hand — and not follow the principle on our daf? The halachic authorities rule that he should indeed put it down and first put on the tefillin for the hand, due to the Torah decree of v’hayu. And to be more careful next time! (Aruch Hashulchan 25:9)

• Pesachim 64b