The mitzvah to observe the Shabbat is given in this week’s Torah portion, the fourth of the 10 commandments: “Remember the Shabbat to keep it holy.” The simple interpretation of this mitzvah, as Rashi explains in his commentary, is “Remember the Shabbat and prepare for her coming every day of the week. For example, if one should come across a fine purchase, set it aside for Shabbat.”
Readying ourselves for Shabbat refer not only to our technical preparations, such as cooking the food and making sure the house is clean. It primarily entails our spiritual preparation: thoughts of Shabbat must occupy our minds all week.
According to the Mishnah, Shabbat refers not only to the seventh day of each week, but also to the seventh millennium, a time of “peace and rest for all eternity.” With the Redemption we will all merit the ultimate peace of mind and tranquility, when we will be able to devote ourselves to Torah study and service of G-d with no distractions. We are presently in year 5772 since creation, in the final quarter of the sixth millennium. According to halachah it is permissible to accept Shabbat early, on Friday afternoon, provided that three-quarters of the day has passed. Now that we have passed that mark, on the millennial scale, we are ready and able to receive Moshiach in actuality.
(Hitvaaduyot 5744, vol. 3, p. 1961)