Sukkah 38A

שירי מצוה מעכבין את הפורענות. שהרי תנופה שירי מצוה היא ⁠— ועוצרת רוחות וטללים רעים. ואמר רבא: וכן בלולב. רב אחא בר יעקב ממטי ליה ומייתי ליה, אמר: דין גירא בעיניה דסטנא. ולאו מלתא היא, משום דאתי לאיגרויי ביה.

non-essential aspects of a mitzva avert calamity, as waving is a non-essential aspect of the mitzva, since even if one failed to wave the loaves he fulfilled his obligation, and nevertheless it halts harmful winds and dews. And Rava said: And likewise one should conduct himself the same way with a lulav, i.e., one should wave it to and fro and raise and lower it for the same reasons. When Rav Aḥa bar Ya’akov would move the lulav to and fro, he would say: This is an arrow in the eye of Satan, as despite his best efforts, the Jewish people continue to joyously fulfill mitzvot. The Talmud notes: That is not a proper manner of conduct, as it will induce Satan to come to incite him to sin. Gloating due to his victory over the evil inclination will lead Satan to redouble his efforts to corrupt him.

מתני׳ מי שבא בדרך ולא היה בידו לולב ליטול ⁠— לכשיכנס לביתו, יטול על שלחנו. לא נטל שחרית ⁠— יטול בין הערבים, שכל היום כשר ללולב.

Mishnah: With regard to one who was coming along the way and did not have a lulav in his hand to take and fulfill the mitzva while traveling, when he enters his house to eat, he should take the lulav at his table. He interrupts his meal to fulfill the mitzva of lulav. If he did not take the lulav in the morning, he should take it in the afternoon, as the entire day is suited for fulfilling the mitzva of lulav.

גמ׳ אמרת, נוטלו על שלחנו; למימרא דמפסיק? ורמינהי: אם התחילו ⁠— אין מפסיקין! אמר רב ספרא: לא קשיא, הא ⁠— דאיכא שהות ביום, הא ⁠— דליכא שהות ביום.

Talmud: The Talmud analyzes the Mishnah. On one hand, you said that if he did not take the lulav before the meal then he takes it at his table. That is to say that if remembers that he did not yet take the lulav, he interrupts his meal, takes the lulav, and then continues his meal. And the Talmud raises a contradiction from a Mishnah (Shabbat 9b): One may not begin to eat before he recites the afternoon prayer; however, if they started a meal, they need not interrupt the meal in order to pray. Rav Safra said: This is not difficult, as that Mishnah, where one need not interrupt his meal, is referring to a case where there is opportunity to pray later in the day; this Mishnah, where one must interrupt his meal, is referring to a case where there is no opportunity to take the lulav later in the day. In that case, one must fulfill the mitzva immediately.