72:3 The book of Isaiah (56:2) praises those who keep Shabbos. It says, "Happy is the man who does this and the person who holds fast to it - the one who keeps Shabbos and does not desecrate it." One who observes Shabbos properly, following its laws, honoring it and taking pleasure in it as best he can, will enjoy the rewards in this world in addition to the great rewards put aside for him in the World to Come. As Isaiah continues (58:13-14), "If you restrain your steps because of Shabbos and refrain from attending to your desires on My (i.e., G-d's) holy day, and if you call Shabbos a delight to Hashem, and you honor it by abstaining from your normal activities by not pursuing your affairs or speaking of mundane matters, then you will delight in Hashem and I will cause you to ride on the high places of the Earth and I will nourish you with the heritage of your father Jacob. This has been said by Hashem."
72:4 The Torah tells us (Exodus 20:8), "Remember Shabbos to keep it holy." This means that one should remember Shabbos on every day of the week and do something to sanctify it. For example, if an especially desirable food item became available, one should buy it for Shabbos, assuming that it will stay fresh until then. It is a mitzvah to get up early on Friday to buy the things that one needs for Shabbos. One may even purchase these things before Shacharis so long as it will not keep him from being able to daven with a minyan. It is preferable to buy things for Shabbos on Friday in honor of Shabbos rather than on Thursday, but if something requires more time in its preparation, then it should be bought on Thursday. When one purchases something for Shabbos, he should say, "l'kavod Shabbos" ("in honor of Shabbos"). Ezra instituted that laundry should be done on Thursday in honor of Shabbos, not on Friday, because people are busy with Shabbos preparations on Fridays. (When the days are short, other preparations should also be made on Thursdays – Mishnah Brurah 250:2.)