The Torah declares in (Exodus 12:16), "On the first day, a calling of holiness." The Mekhilta asks what it actually means to "call" a day holy — and the answer is surprisingly concrete.
Sanctify it with food and drink and with clean clothing. Holiness, in the rabbinic understanding, is not purely spiritual or abstract. It is expressed through the body: what you eat, what you drink, what you wear. A holy day looks different, tastes different, and feels different from an ordinary day. This is the foundation of Jewish festival observance — that sanctity takes physical form.
But a harder question follows. The verse explicitly names only the first and last days of Passover as "callings of holiness." What about the intermediate days — chol ha-moed — which fall between the sacred bookends? Are they merely ordinary weekdays that happen to occur during a festival?
The Mekhilta turns to (Leviticus 23:38), which states, "These are the festivals of the Lord, which you shall call callings of holiness." The word "these" encompasses the entire festival period, not just its endpoints. The intermediate days are also "callings of holiness," carrying their own sanctity — even if it operates at a different level than the first and last days.
The practical result is that chol ha-moed is neither fully sacred nor fully mundane. It occupies a unique middle space in the Jewish calendar — days touched by holiness but not wholly consumed by it.