A direct quote from the Torah (Exodus 31:16-17), the following two verses are often recited aloud as part of the Friday night service. It is a reminder that Shabbat is a sign of the covenant between God and the Jewish people.
V’shamru v’nay Yisrael et ha’Shabbat, la’asot et ha’Shabbat l’doh’ro’tam b’reet olam. Bay’nee u’vayn b’nay Yisrael oat hee l’olam, kee shay’shet yameem a’sah Ah’doh’nai et ha’sha’ma’yim v’et ha’aretz, u’va’yom ha’sh’vee’ee shavat va’yee’nafash.
The children of Israel must keep the Sabbath, observing the Sabbath in every generation as an everlasting covenant. It is a sign between Me and the children of Israel forever, for in six days God made the heavens and the earth, but on the seventh day He ceased work and refreshed Himself.
--Translation reproduced with permission from The Koren Sacks Siddur, © Koren Publishers Jerusalem Ltd.