Mesirus nefesh prepares for the holiness of the festivals

הבנתי מדברי קדשו של אא"ז ז"ל בסמיכות מצות ונקדשתי בתוך בנ"י למועדים.

I understood from the holy words of my grandfather, of blessed memory, regarding the juxtaposition of the mitzvah of "And I shall be sanctified among Bnei Yisrael" (Vayikra 22:32) to the parsha of the Moadim (festivals).

The Sefas Emes notes that the Torah places the command of "v'nikdashti b'soch Bnei Yisrael" — the obligation of kiddush Hashem (sanctifying Hashem's Name) — right next to the laws of the festivals, and learns a lesson from this proximity in the name of his grandfather, the Chiddushei HaRim.

כי ע"י מס"נ על ג' עבירות יכולין לקבל קדושת המועדים שהם מכוונים הג' רגלים לג' עבירות הללו ונק' מקראי קודש והכנה לקבל הקדושה עי"ז להיות מוכן למס"נ בעבורו ית' כמ"ש ונקדשתי:

For through mesirus nefesh (self-sacrifice) regarding the three cardinal sins, one is able to receive the holiness of the festivals — for the three regalim correspond to these three sins — and they are called mikra'ei kodesh (holy convocations) and a preparation to receive that holiness; through this one becomes ready for mesirus nefesh for His sake, as it says "And I shall be sanctified."

The three festivals (Pesach, Shavuos, Sukkos) parallel the three sins for which a Jew must give up his life rather than transgress — avodah zarah, gilui arayos, and shefichus damim. By being prepared to give one's life to sanctify Hashem's Name, a person becomes a fit vessel ("mikra'ei kodesh") to absorb the holiness that each Yom Tov radiates. The readiness for kiddush Hashem is itself the hachanah (preparation) for the kedushah of the Moadim.

Summary: The Torah juxtaposes the mitzvah of kiddush Hashem to the festivals to teach that the three regalim correspond to the three cardinal sins; a Jew's readiness for mesirus nefesh to sanctify Hashem's Name is the very preparation that makes him a vessel to receive the holiness of the Moadim.