Why does the Torah juxtapose Pesach to Avodah Zarah?
Seforno: After forbidding turning to molten images to attain success in this world, 1 the Torah presents the correct method of attaining success - with regard to the ripening, the harvesting and the ingathering of one's crops and the acquiring of wealth. 2
Da'as Zekenim, Hadar Zekenim and Rosh (in Pasuk 17): It serves a warning against concocting a new festival, like they did by the Eigel, when they declared "Chag la'Hashem Machar", and against initiating a day for idolatry, but rather, to observe the Yom-Tov of Pesach, which Hashem commanded us to observe.
Pesachim, 118a: To teach us that if someone treats Yom-Tov (Chol ha'Mo'ed) lightly, it is as if he worshipped Avodah Zarah. 3
Yerushalmi, Chagigah 3:1: The Torah juxtaposes "es Chag ha'Matzos Tishmor" to Avodah Zarah, to teach us that if someone is capable of declaring a leap-year 4 and fails to do so, it is as if he worshipped Avodah Zarah.
Oznayim la'Torah (on Pasuk 22): The Torah juxtaposes Pesach and the Yamim Yovim to Avodah Zarah to teach us that the Yamim-Tovim create a safeguard against Avodah Zarah, 5
What is the reason for the sequence of the Mitzvos listed in the current Pesukim?
Seforno: a. Pesach - which brings a B'rachah to the crops as they ripen; b. B'choros - a B'rachah on one's flocks; c. Shabbos - a B'rachah for the week, and Sh'mitah - for the other six years of the cycle; d. Shavu'os - a B'rachah on the harvest of the crops e. Sukos - a B'rachah for the ingathering of the crops, followed by the Mitzvah of going to Yerushalayim on Yom-Tov, pertaining to all the Shalosh Regalim. And f. the Torah presents Mitzvos that pertain to Pesach 1 and that apply to the seasons of Shavu'os 2 and of Sukos. 3
