Yom HaKippurim - Attitude of the Day
Yom HaKippurim carries the commandment of self-mortification, which follows after the commandment of rest (Wayyiqra' [Leviticus] 23:32). The mortification required on Yom HaKippurim consists of abstention from food and drink, since all mortification mentioned in connection with the soul signifies fasting (Tehillim [Psalms] 35:13; Yesha‘yahu [Isaiah] 58:10). This means that everything that is connected with eating is also forbidden on that day, such as touching cooking
There is doubt among some as to whether the mortification mentioned in connection with the soul infers fasting. They say that if
this were so, there would have been no need to say, "I have afflicted my soul with fasting." It would have been sufficient to say, "I have mortified my soul." This would have implied fasting, assuming that all mortification connected with the soul signifies fasting. This, however, is not a valid argument. "With fasting" serves to express the idea with greater detail - it expands and defines the notion of mortification.
It is granted that the literal meaning of the words, "to mortify the soul," does
not refer exclusively to fasting, but to anything whereby the soul is mortified, as in "Every vow and every binding oath to afflict the soul"
(BeMidbar [Numbers] 30:14), where fasting is not expressly mentioned, nevertheless in
actual usage of the Hebrew language, we do not find this expression employed except with particular reference to fasting (c.f. Yesha‘yahu 58:3).
While mortifying one's soul, one should concentrate one's heart on repentance, for fasting without heart-felt repentance is useless. This is why
the Miqra' [Scripture] connected mortification with the soul.