ויקרא

ופתח אהל מועד תשבו יומם ולילה שבעת ימים. הזהירם שלא יצאו מפתח אהל מועד יומם ולילה בשעת עבודה, כלומר עד שישלימו כל העבודה המוטלת עליהם באותו העת, והיא מצוה נוהגת לדורות שלא יניח כהן עבודה ויצא וזהו שאמר בכהן גדול (ויקרא כא) ומן המקדש לא יצא ולא יחלל, אימתי אינו יוצא ואינו מחלל הוי אומר בשעת עבודה, ואם עשה כן חייב מיתה, שנאמר פן תמותו, ומכלל לאו אתה שומע הן.

ופתח אהל מועד תשבו יומם ולילה שבעת ימים, “and at the entrance of the Tent of Meeting you shall dwell for seven days.” Moses warned the Priests not to leave the proximity of the entrance of the Tent of Meeting at the time they performed the service, i.e. until they had completed all the parts of the service which they were meant to perform at that time, i.e. on that occasion. This commandment remained in force not only during the days of the inauguration but for all future times. This is the meaning of the verse (Leviticus 21,12) “he shall not leave the Sanctuary so that he will not desecrate the Sanctuary of his G’d.” The answer to the question of when not leaving the Sanctuary ensures that the Sanctuary will not be desecrated is: “during the time the service is in progress and has not been completed.” If the Priest were to leave the Sanctuary during this time he would commit a capital crime and would be liable to die at the hands of G’d. This is an instance where the negative commandment which is spelled out, i.e. not to leave the holy precincts, allows for a halachically valid inference that if the party concerned does the reverse, i.e. leave the holy precincts during this time, he is guilty of death. [In practice this means that when the High Priest has become an אונן, lost a close relative who has not yet been buried, he must not leave the Sanctuary and leave the performance of the service to a substitute. Ed.]

ומה שהזהירם שלא יצאו מן הפתח לא ביום ולא בלילה, כוונת הפסוק בשעות הראויות לישב שם, שהרי בשר ודם הוא מוכרח לעשות הענינים הגופניים, כיוצא בו אמר הכתוב בבנין ביהמ"ק (מלכים א ו׳:ל״ח) ויבנהו שבע שנים, ואת ביתו בנה שלמה י"ג שנה, שאין לכלול בהם השבתות והמועדים, כי הכוונה בימים הראויים למלאכה, אף כאן הזהירם שלא יצאו מן הפתח בשעות הראויות לישב שם.

The meaning of the words יומם ולילה, “both by day and by night,” is not an absolute statement meaning: “around the clock.” It means that during the hours when a Priest is supposed to be on duty in the Sanctuary (or adjoining it) he must not leave these precincts regardless of whether it is night or day. Seeing that every human being sometimes has to answer calls of nature, the Priest is not only allowed to do so but commanded to do so. The Torah refers to times when there is no such call of nature which would provide a legitimate excuse for the Priest to temporarily absent himself. We find parallel meaning of the words “seven years” in connection with the building of Solomon’s Temple (Kings I 6,38-7,1) “He built it for seven years; and it took him thirteen years to build his palace until his whole palace was completed.” The prophet means that it took this number of years to build excluding the Sabbaths and festivals on which no work was performed. Just as these days were excluded in the prophet’s summation of how long it took to build the Temple, so here too the time out when a Priest had to answer a call of nature was excluded when the Torah spoke about “day and night.”

ובמדרש ופתח אהל מועד תשבו יומם ולילה אלו שבעה ימים אבלות של נדב ואביהוא, שהרי הקב"ה שמר על עולמו תחילה. באורו שהתאבל שבעה ימים על העולם שעתיד ליחרב בדור המבול, שנאמר (בראשית ז) ויהי לשבעת הימים ומי המבול היו על הארץ. ואמרו שם ומתאבלין על המת קודם שימות, אלא אדם שאינו יודע מה שעתיד להיות אינו מתאבל עד שימות המת אבל הקב"ה שיודע מה שעתיד להיות שמר על עולמו תחלה, אף כאן אמר הקב"ה ופתח אהל מועד תשבו יומם ולילה שבעת ימים, שמרו על אחיכם שבעה כדרך ששמרתי אני את עולמי שבעה, וזהו שכתוב ושמרתם את משמרת ה'.

A Midrashic approach based on (Tanchuma Shemini 1): when the Torah speaks of “and you shall remain at the entrance of the Tent of Meeting day and night,” this is a reference to the seven days of mourning for the deaths of Nadav and Avihu. While it is true that at that point in time these two sons of Aaron had not died as yet, we know that G’d Himself observed seven days of mourning for an event which had not yet occurred. This was the reason that the Torah wrote in Genesis 7,10: “it was after the seven days, and the waters of the deluge came upon the earth.” G’d had observed seven days of mourning over the necessity that He had to destroy so much of His handiwork. In connection with that verse, the sages asked: “can one then mourn someone before he died?” If such a thing is not possible or not appropriate why did G’d mourn the event before it happened?” Man who does not know what is in store in the future cannot mourn an event which has not yet occurred. G’d who does know, is able to do so. In our instance, G’d told Aaron and his sons to observe seven days of a special nature although they were not aware of the reason. He wanted them to act as He had acted prior to the deluge. This is why the Torah wrote the words 'ושמרתם את משמרת ה, “you shall observe the observance observed by the Lord.” [If I understand this Midrash correctly, Nadav and Avihu sat in mourning of their own deaths prior to it having occurred. It would prove that Nadav and Avihu’s death had already been decreed prior to their taking “alien fire” into the Sanctuary, i.e. something unbidden, that this was only the occasion which determined when G’d’s decree would be carried out. Ed.]