The observation of the Sabbath, or more appropriately Shabbat in Hebrew, is an important devotional aspect of Judaism. It is derived from the original 10 Commandments given Moses and the nation of Israel at Mt. Sinai, as recorded in the Biblical Book of Exodus. God commands the Jews to observe the day weekly (Saturday) and to abstain from the normal toils and worldly or temporal concerns that typify the rest of the week. We remember that this commandment is reminiscent of God's decision to rest after the week of Creation, after seeing all that was made was "good," as recorded in Genesis.
While there are undoubtedly more complex and deeper theological interpretations associated with this issue, it is important to recognize that which is simple: Shabbat is a welcome time for many Jews to rest, contemplate and reflect upon their relationship with God, and to make some room for Him in their busy lives.
Hope this helps, and very best wishes!