Siman - Megillah Daf 20
- The sources for mitzvos that must be performed during the day
The next Mishnah states: אין קורין את המגילה ולא מלין ולא טובלין ולא מזין וכן שומרת יום כנגד יום לא תטבול עד שתנץ החמה – We do not read the Megillah, nor circumcise, nor immerse in a mikveh, nor do ha’zah, and similarly, a shomeres yom k’neged yom may not do tevillah, until the sun has risen. וכולן שעשו משעלה עמוד השחר כשר – And all of them, if they did the mitzvah after the first ray of dawn has appeared, it is kosher. The Gemara brings the source for each, that it must be performed during the day. Regarding the Megillah, the passuk states: "והימים האלה נזכרים ונעשים" – And these days should be remembered and celebrated, which implies that the Megillah must be read during the day and not at night. The Gemara clarifies that the Mishnah is not a contradiction to Rabbi Yehoshua Ben Levi, who rules that the Megillah must be read at night as well, as the Mishnah can be understood to be referring to the Megillah reading of the day . Circumcision is done during the day, as the passuk states: "וביום השמיני ימול" – And on the eighth day you shall circumcise. Tevilah and haza’ah are done during the day, as the passuk states: "והזה הטהור על הטמא...ביום השביעי" – And the tahor person shall sprinkle on the tamei person…on the seventh day. We see from here that the haza'ah must be done during the day, ואיתקיש טבילה להזיה – and then we make a hekesh between tevilah and haza’ah and learn that tevilah too must be done during the day .
- The source that amud hashachar is the start of day
The Mishnah had stated: וכולן שעשו משעלה עמוד השחר כשר – And in all these cases, if they did the mitzvah from the first ray of dawn, it is kosher. The Gemara asks for the source that the day begins with the first ray of dawn, and after it rejects the first answer, it brings Rebbe Zeira, who said that the source is the passuk, "ואנחנו עשים במלאכה וחצים מחזיקים ברמחים מעלות השחר עד צאת הכוכבים" – Then we did the work, with half of them holding spears, from the first ray of dawn until the stars came out, and it states in the next passuk: והיו לנו הלילה משמר והיום מלאכה – We spent the night on watch, and the day at work. The Gemara clarifies that the second passuk was brought, since one might have said, from the first passuk we can say that amud hashachar comes before the day, and is not considered day, and when the sun sets it is night, and the workers mentioned began their work before day began and stayed at work later than nightfall. Therefore, the second passuk states: "והיו לנו הלילה משמר והיום מלאכה", to teach that when the workers began working at amud hashachar it was considered day.
- Daytime mitzvos and nighttime mitzvos
The next Mishnah lists twenty mitzvos that may be performed the entire day, and then lists two mitzvos that are kosher the entire night, קצירת העומר ולהקטיר חלבים ואברים – reaping the Omer and burning the fats and limbs of the offerings. The Mishnah concludes, זה הכלל – This is the general rule: דבר שמצותו ביום כשר כל היום דבר שמצותו בלילה כשר כל הלילה – Any mitzvah that must be done during the day, may be performed anytime during the day, and any mitzvah that must be done at night, may be performed anytime during the night. The Gemara brings the sources for each of the mitzvos, to prove that they are either daytime mitzvos or nighttime mitzvos.
