And Shall Guard
Vesham'ru v'nei Yisarel et haShabbat laasot et haShabbat l'dorotam b'rit olam
And the Children of Yisrael shall keep the Sabbath, to make the Sabbath an eternal covenant for their generations.Benei uvein benei Yisarel ot hi l'olam ki sheshet yamim asah Hashem et hashamayim v'et ha-aretz uvayom hash'vi'i shavat vayinafash
Between Me and the Children of Yisrael it is a sign forever that in six days Hashem made heaven and earth, and on the seventh day He rested and was refreshed.
This passage is from Shemot 31:16-17 of Yisrael's Shabbat observance and is related to the theme of redemption, because Yisrael will be redeemed from exile in the merit of Shabbat observance (Abudraham).
The verse for the pilgrimage festivals alludes to the freedom from Egypt.
This chapter of Shabbat observance appears in the Torah immediately after the commandment to commence the construction of the Tabernacle. This teaches that even for the sake of building the Temple, one may not desecrate the Shabbat (Rashi) By logical extension, this concept refutes those who may tend to relax the observance of the Shabbat or other mitzvot for the sake of what they consider to be noble spiritual causes.
Sources:
Artscroll Siddur
The Art of Jewish Prayer