It is a mitzva to honor Shabbat, as it is written: “Call Shabbat ‘delight,’ the Lord’s holy [day] ‘honored’” (Yeshayahu 58:13). Part of honoring Shabbat is making sure that one does not dress on Shabbat as he would during the week (Shabbat 113a). Rather, Shabbat clothes should be nicer and clean. Some authorities write in the name of Arizal that it is best not to wear anything on Shabbat that one has worn during the week (MA 262:2). This means that one’s outer garments should be special for Shabbat and Yom Tov, and one’s undergarments should be freshly laundered. Some buy special shoes for Shabbat as well (see SSK ch. 42 n. 206). One who is spending Shabbat alone should still dress up, because the clothes are not meant to honor the people who see them, but to honor Shabbat (MB 262:6).
One who unexpectedly finds himself somewhere for Shabbat and does not have Shabbat clothes available, or a poor person who owns only one garment, should do his best to make his clothing look nicer before Shabbat. Thus we read in the Yerushalmi that R. Simlai publicly taught that everyone should have two sets of clothing, one for weekdays and one for Shabbat. His students cried, saying: “We are poor and we have only one garment.” He said to them: “Nevertheless, you must beautify it before Shabbat” (y. Pe’ah 8:7). Thus soldiers must wear their dress uniforms on Shabbat, and if that is not possible they must clean their clothes and make them look as best they can.
One of the ten ordinances instituted by Ezra the Scribe is that clothing be washed on Thursday (BK 82a). There are two reasons for this ordinance: first, one should not wear dirty clothes on Shabbat. Second, since laundering was hard work, it was ordained to be done on Thursday, so that people would have time to cook and to clean the house on Friday. Nowadays, however, when washing is done by machine, one may do laundry on Friday because it is not too burdensome and it does not disrupt Shabbat preparations. Nevertheless, it is preferable that Shabbat clothing be washed on Thursday, in accordance with Ezra’s ordinance.
We can generalize from Ezra’s ordinance that one should be careful not to turn Friday into a day full of hard and aggravating work. Rather, Friday should be left relatively free, so that people can prepare for Shabbat in a relaxed and calm way (as explained in section 2 above).