At the conclusion of each of the first six days of creation, the Torah states, “Vayehi Erev Vayehi Voker,” that a night and a day passed. The Torah Temimah asks: why does the Torah not also say this concerning the seventh day of creation?
He cites the Talmud Yerushalmi in Berachot 8:5, which quotes Rabi Levi in the name of Rabi Bezeirah, who answers that the sun shined for 36 hours straight, from Friday morning until the end of Shabbat. Hashem did this because he wanted to refrain from creating Shabbat evening and Shabbat morning.
The Yerushalmi adds that when Adam first saw darkness on Motza’ei Shabbat, he became extremely fearful, for the sun had shone continuously throughout his short life. Rabbi Levi says Hashem presented Adam with two flint rocks to rub together and create light. Furthermore, Shmuel adds that the reason we make Havdalah on a fire after every Shabbat is to signify that Motza’ei Shabbat commemorates the creation of fire.
The only other day on which we cannot use fire is Yom Kippur. Shmuel’s reason for making Havdalah on Shabbat does not apply to Yom Kippur when it falls out on a weekday. In this case, we follow the opinion of Rav Huna quoting Rabi Avahu quoting Rabi Yochanan, who says we can make Havdalah with fire for a second reason – to commemorate the fire’s resting over Yom Kippur. For this reason, we go out of our way to make Havdalah on a candle lit throughout Yom Kippur, because this Havdalah commemorates our renewed use of fire following Yom Kippur.