The Seventh Day of the Jewish Week.

God instructed Israel to keep every seventh day 'holy'-a day of rest in which Israel would do no work but reflect on the blessings they enjoyed at God's hand.

"For in six days the LORD made the heavens and the earth, the sea and all that is in them, but he rested on the seventh day. Therefore the LORD blessed the Sabbath day and made it holy." (Exodus 20:11).
Violations of the Sabbath were punished with death. During Israel's desert wanderings God contributed to the rest on the Sabbath by providing additional 'manna' (food) on the sixth day which kept fresh on the seventh day. Every seventh year was also a sabbath year in which the land was not to be cultivated. The harvest of the sixth year by God's gracious provision, was always sufficient for the seventh year, and provided seed for the eighth year also. In this way Israel were continually reminded of God's ability to provide for them.

The people of Israel were sent into captivity because they disobeyed, among other things, God's Sabbath laws, and in Israel's absence, the land "enjoyed her sabbaths" (see Leviticus 26:34,43).
There is no requirement for Christians to observe the Sabbath. "For he [Christ] himself is our peace, …abolishing in his flesh the law with its commandments and regulations." (Ephesians 2:14-15). "He who loves his fellowman has fulfilled the law." (Romans 13:8).

God rested on the seventh day from His work of creation (see Genesis 2:2), and the writer to the Hebrews tells us: "The promise of entering His rest still stands…there remains, then, a Sabbath-rest for the people of God…. Let us, therefore, make every effort to enter that rest." (Hebrews 4:1,9,11).