The Gemara in Masechet Shabbat (25b) tells that Rabbi Yehuda Ben Rabbi Ilai, one of the greatest of the Tanna’im, would have hot water brought to him on Ereb Shabbat, and wash his face, hands and feet in honor of Shabbat. On the basis of this account, the Shulhan Aruch (Orah Haim 260) writes that there is a Misva to wash at least one’s face, hands and feet with hot water before Shabbat. It should be noted that if a sage of Rabbi Yehuda Ben Rabbi Ilai’s stature took time away from his Torah study to bathe before Shabbat, then we must conclude that this constitutes a very important Misva.
Indeed, the Arizal (Rabbi Yishak Luria, 1534-1572) was very strict with regard to this Halacha, and made a point of bathing with hot water every Ereb Shabbat. He would have in mind different Kavanot (mystical ideas) as he bathed, demonstrating the spiritual significance of this Misva. The Arizal held that one should wash first his face, followed by his right hand, left hand, right foot and left foot, in that sequence. One should follow this sequence even if he takes a full shower.
Additionally, the Arizal maintained that one should wash specifically with hot water, even during the summer months.
The Mishna Berura (Rabbi Yisrael Meir Kagan of Radin, 1839-1933) issued an important warning concerning bathing on Ereb Shabbat in the winter. Shabbat during the winter months begins early on Friday afternoon, and people are often rushing to complete their Shabbat preparations on time. Particularly on short Fridays, one must exercise care to ensure that he finishes bathing before the onset of Shabbat. It is forbidden to bathe with hot water on Shabbat, and a person who is not careful may end up violating Shabbat even as he seeks to perform the Misva of honoring Shabbat. One must therefore make a point to ensure that he finishes bathing before Shabbat begins.
Summary: It is a Misva to bathe at least his face, hands and feet with hot water on Ereb Shabbat. One should first wash his face, followed by his right hand, left hand, right foot and then left foot. One must be very careful to ensure that he finishes bathing before the onset on Shabbat, as bathing with hot water is forbidden on Shabbat.
