Having already informed us how the two pillars led Yisrael by day and by night, why does the Torah add this Pasuk?
Rashi: To teach us that, after the pillar of fire arrived, the pillar of cloud remained for a short while before departing, and vice-versa. 1
QUESTIONS ON RASHI
Rashi writes: "'Lo Yamish' - [I.e.,] Hashem [did not cause] the pillar of cloud or the pillar of fire to be removed ...." What is Rashi clarifying?
Gur Aryeh: The verb "Yamish" is in Hif'il (causative) form. Had the verse meant that the pillars themselves did not leave, it should have said 'Yamush,' in Kal form. 1
Rather, "Lo Yamish" means that Hashem (the subject in the previous verse) did not allow them to leave. See Gur Aryeh, as to why this example differs from the verse "Yehoshua ... Lo Yamish [mi'Toch ha'Ohel]" (Shemos 33:11).
Rashi writes: "... The pillar of cloud would supplement the pillar of fire... Before one set, the other would rise." Why was this the case?
Mechilta: It is from here that we learn that one should begin to bring in Shabbos (a short time) before nightfall. 1
Maharal (Chidushei Agados Vol. 1, p. 7, to Shabbos 23b): The two pillars working together showed how both came from Hashem, Who is One. That way, it would not give the appearance of coming from 'two powers.' 2
Oznayim la'Torah: So that Yisrael should not be for even one moment without Divine protection.
See Torah Temimah, note 80, who elaborates.
Maharal: This idea is also reflected in Halachah. In the blessings preceding Keri'as Shema in the morning (Yotzer Or), we must also mention the darkness of night (... u'Vorei Choshech); and at night (Ma'ariv Aravim) we also mention the light of day (... v'Choshech mi'Pnei Ohr).
