The Body Follows the Head – Eruvin 41a
תלמוד בבלי מסכת עירובין דף מא/א
עמד רבי יוחנן בן נורי על רגליו ואמר חזי אנא דבתר רישא גופא אזיל
The statement that "after the head, the body follows has been used in many contexts of Jewish thought.
- The beginning of a month is called Rosh Chodesh, not Techilas Chodesh in order to indicate that it commences the particular Avodas Hashem associated with that month, and encapsulates the specific kedusha associated with that month (Pri Tzaddik, Chanukah §15). Hence, on any Rosh Chodesh one should sense the qualities of the Yom Tov that occurs during that month (ibid., Parashas HaCodesh §6).
- The first of Nisan is called Rosh HaShanah L'Regalim because the kedusha of all the Yomim Tovim is encapsulated in Nisan. That is why the Torah calls this month Rosh Chodashim — the head of all the months (ibid., Parashas HaChodesh §2).
- In a similar vein, the beginning of a year is called Rosh HaShanah because the course of the entire year is determined according to what transpires on Rosh HaShanah (ibid., Rosh HaShanah §3).
- In Bava Basra (121a) on the Gemara that states that Yomim Tovim, as Mikraei Kodesh, require Kiddush Beis Din, the Rashbam states that this takes place when the Beis Din pronounces "Mekudash, mekudash" on Rosh Chodesh. This is because the Rosh Chodesh encapsulates the kedusha of the subsequent Yom Tov (ibid., Emor §4).
- It is also for this reason that whenever the Torah pegs the date of Yom Tov it states it as X days "bachodesh" — because the kedusha of the Yom Tov already "came down" on Rosh Chodesh (ibid., Sivan §3).