את ועשית ושמרת במצרים היית עבד כי וזכרת” (יב טז) “האלה החקים
This passuk that instructs the remembrance of Yetzias Mitzrayim is said after the commandment to celebrate Shavuos. We need to learn from this that not only Pesach and Succos were set to remember Yetzias Mitzrayim. Shavuos, which is considered a continuation of Pesach (see Ramban Vayikra 26:33) was also instated as such. Indeed, the Likutei Maharich wrote that this passuk is the source that we say in Kiddush and the tefillah on Shavuos “Zman Mattan Toraseinu mikra kodesh zecher l’Yetzias Mitzrayim.”
Harav Shlomo Zalman Auerbach explained that this is why we mention the name of each holy day at the end of the brachah said in its honor [Mekadesh HaShabbos, Roshei Chodashim, Yom Hazikaron and Yom Hakippurim], while on each of the Shalosh Regalim we conclude the brachah with the same nusach: “Mekadesh Yisrael vehazmanim,” without detailing the name of the Yom Tov. This is because all the regalim were instituted for the same reason – “zecher l’Yetzias Mitzrayim,” and that is why there is a single nusach for the three of them.
Likutei Maharich Seder Minhagei Chag Hashavuos; Minchas Shlomo Beitzah 17a
