The Sages state that it is a mitzva to set the table on Saturday night for the melaveh malka (lit. “accompanying the queen”) meal, with which we honor Shabbat at its departure (Shabbat 119b). When one must say goodbye to a dear and beloved guest whom he does not want to leave, he escorts him a distance in order to spend just a bit more time with him. So too, we must escort Shabbat at its departure. Despite the fact that it is over, we continue to savor and delight in its holiness.
On Shabbat we are blessed with additional holiness in all areas of life, material and spiritual, as expressed through prayer and meals. Our goal is to extend the light of Shabbat to the weekdays. Arizal explains that by saying Vi-yhi No’am (Tehilim 90:17–91:16) in Ma’ariv on Saturday night, we extend the additional spiritual holiness of Shabbat to the weekdays, and ask that God’s grace rest upon all our endeavors. Through melaveh malka we extend the light of holiness to our eating all week.
We have a tradition that there is a bone in the human body called the luz. This bone did not benefit when Adam ate from the Tree of Knowledge; therefore, even though death was decreed upon mankind as a result of the sin, this bone does not rot. At the time of the resurrection of the dead, each individual’s revival will begin from the luz. This bone, we are told, is nourished only by melaveh malka (Kaf Ha-ĥayim 300:1-2; Vayikra Rabba 18:1).
Those who are especially devout prepare special food for melaveh malka. The Talmud (Shabbat 119b) recounts that R. Abahu’s household was accustomed to slaughter a calf on Saturday night to serve at the melaveh malka. R. Abahu would eat one of its kidneys. When R. Abahu’s son grew up, he asked why it was necessary to slaughter an entire calf each Saturday night. He suggested that it made more sense to leave over a kidney from the calf that had been slaughtered on Friday, and eat that on Saturday night. The family listened to him and saved some of Friday’s meat for Saturday night. A lion came along and devoured the veal that was meant for Saturday night. Thus they gained nothing. The Gemara tells us this story to teach us that it is proper to make the extra effort and prepare special food for melaveh malka rather than just eat Shabbat leftovers.