“Such is the way of Torah: Bread with salt you shall eat, water in small measure you shall drink.”
Does this mishnah mean that a person who studies Torah and wants to merit the crown of Torah has to fast, afflict himself, and be an ascetic? No! On the contrary. The sages teach that anyone who fasts for no real reason is called a sinner. This especially pertains to a Torah scholar, if the fast makes it difficult for him to study Torah. It is told that when the Lubavitcher Rebbe, Rabbi Menachem Mendel Schneersohn was young, he would abstain from eating until after the afternoon prayers. When his father, Rabbi Levi Yitzchak found out, he convinced him to stop.
What then, is the point that this mishnah is making? Rashi explains: “Even if a person has nothing more than a piece of bread with salt, …he should not abstain from studying Torah, for ultimately he will study in wealth.” Furthermore, a person who is immersed in Torah has no time to immerse himself in material pleasures. “A tzaddik should eat for the satiation of his soul,” no more and no less.
In the prayers of the High Holidays we say, “And teshuvah (return to God) and prayer and charity annul the negative decree.” In the prayer books, above each of these three—teshuvah, prayer, and charity—there is a small word written. Above teshuvah, we find the word for “fast”; above prayer, we find the word for “voice”; and, above charity, the word for “money” is written. The numerical value of these three words—fast (צוֹם), voice (קוֹל), and money (מָמוֹן)—is identical: 136.
The three dynamics of teshuvah, prayer, and charity correspond to the three pillars—Torah, service of God, and acts of loving-kindness—upon which the world stands. Specifically, prayer corresponds to the service of God. Charity clearly corresponds to acts of loving-kindness.
Finally, teshuvah parallels the pillar of Torah. There are in principle two forms of teshuvah known as higher and lower. The higher form of teshuvah, great love and passion to become subsumed within the Divine, entails cleaving to God by means of Torah study. Higher teshuvah corresponds to the upper hei of God’s Name, Havayah, and to the sefirah of understanding.
Indeed, as taught in the Zohar, the word teshuvah (תְּשׁוּבָה) can be read as, “return to the hei” (תָּשׁוּב ה) alluding to a return to the letter hei in God’s four-letter essential Name, Havayah. “Higher teshuvah” (תְּשׁוּבָה עִלָּאָה), thus means a return to the higher (first) hei of God’s Name. Thus, the “fast” belonging to the higher form of teshuvah is not a fast to repent for sins. Rather, it is a fast of, “eat bread with salt.” The salt represents curtailment and sufficing oneself with just the bare minimum. When a person studies Torah, he cleaves to God and contracts himself (like the salt in his fast) into the “four cubits of Jewish law.” The four cubits of Jewish law correspond to the four letters of God’s Name. In this state of “fasting,” he is ensconced in the upper hei and in a state of constant higher teshuvah.
 Taanit 11a.
 Likutei Levi Yitzchak p.443.
 Proverbs 13:25.
 Taanit 2a.
 See Tanya, Igeret Hateshuvah, ch. 9 and on.
 Brachot 8a.
 Shabbat 153a.