Rashi: Because it is on condition that you keep these Mitzvos that Hashem took you out of Egypt.

Ramban #1 (citing the Ibn Ezra): With reference to "Avd'cha va'Amascha" in the previous Pasuk, the Torah is reminding us that we too, were once Avadim in Egypt. (Consequently, just as Hashem helped us, so too, should we help our Avadim Ivrim).

Ramban #2: It means simply that we should observe all these Chukim that Hashem, who redeemed us from Egypt, commanded us. ¹

Seforno: To remind us that when we were Avadim in Egypt we had nothing of our own, and that we should therefore acknowledge that Hashem gave us wealth and property - by leaving Leket and Pe'ah, to find favor before Hashem.

Sifri: To teach us that the Mitzvah of Simchah extends to Pesach and Sukos ² - since they too, commemorate Yetzi'as Mitzrayim.

Ramban: Because the Torah did not give us a reason for the seven weeks (fifty days) from the Omer until Shavu'os.

Seforno: It is referring to the Mitzvos of Leket and Pe'ah - Refer to 16:1:1:4.

Ba'al ha'Turim: It is referring t all the Mitzvos of the Torah, and it mentions them by Shavu'os because that is when the Torah was given.

Sifri: With reference to 16:2:1:5, it teaches us that we do not compare Shavu?os to Pesach and Sukos and that Matzah, Sukah, Lulav and Shiv?ah (seven days) do not apply on Shavu?os. ¹

Riva citing R"M of Kutzi: 'Do not say, how will I ascend [to Yerushalayim] and neglect the harvest? Remember, you were Avadim, and you had nothing, until Hashem graced you (and took you out of Egypt).

Hashem took us from Egypt in order to serve Him (to receive the Torah) on Har Sinai (PF). ¹