A person’s very appearance is different on Shabbat than it is during the rest of the week.

“God blessed the seventh day, and sanctified it” (Genesis 2:3). This means that He blessed it with the glow of one’s face. The glow of a person’s face throughout the week is not like its glow on Shabbat. (Bereshit Rabba [Theodor-Albeck] 11)