From Chabad.org: This section begins a lengthy discussion about the Jewish holidays. After making brief mention of the Shabbat, the Torah talks about the holiday of Passover and the mitzvah of eating matzah. On the second day of this holiday, an “omer” barley offering is brought in the Temple. This is followed by a seven-week counting period that culminates with the holiday of Shavuot. After discussing the Shavuot Temple service, the Torah briefly interrupts the holiday discussion to mention the obligation, when harvesting fields, to leave certain gifts for the poor.
While it may not be the first time the Torah says this, I’ve always found it interesting that when calling a day holy, the Torah says “mikra Kodesh”, which literally means “it shall be called holy”. If a day is described by the torah to be holy, such as it does here for Pesach, wouldn’t it make more sense that the day actually BE holy, rather than just being CALLED holy? Or maybe it’s because we call it holy that it becomes so. Suddenly what seems like an imposition of rules turns into a list of empowerments.