G‑d blessed the seventh day and sanctified it. (Gen. 2:3)
Rabbi Yitzchak said: It is written, "G‑d blessed the seventh day," and regarding the manna it is written, "Six days you shall gather it, but the seventh day is Shabbat; on [Shabbat] there will be none" (Ex. 16:26).
The Shechinah rests only where there is wholeness and completeness….
Since food was not found on that day, in what way is it [Shabbat] blessed? Blessing does not reside on an empty table - there must be some vessel upon which the blessing can descend.
We have learned as follows that all blessings Above [in the Higher Worlds] and Below [in This World] are dependent upon the seventh day.
This is because "the Shechinah rests only where there is wholeness and completeness".
Why was no manna found on that day? Because all the six supernal days [i.e. the six attributes Above: chesed, gevura, tiferet, netzach, hod, yesod] are blessed by it, the final sefira (i.e. malchut), and each of them receives its sustenance down Below [in This World] from the blessing with which the seventh day is blessed.
Setting the table elicits blessing from Above, similar to the laying of the show-bread on the Golden Table in the Temple….
For this reason, a person of faith must set his table and prepare a meal for Friday night, so that his table will be blessed all six days [of the coming] week, for blessing is not found upon an empty table. Accordingly, one must set the table on Friday night with bread and food.
Rabbi Yitzchak said: [One must set the table with bread and food on] the Shabbat day also.
According to both these opinions, setting the table elicits blessing from Above, similar to the laying of the show-bread on the Golden Table in the Temple, not actually partaking of the meal. This can be understood from the fact that it is not a commandment for the Kohens to eat the show-bread - it is merely part of their reward for serving in the Temple. (see Chinuch 97; Smag, aseh 196)
Rabbi Yehuda expressed [a third view]: One must delight in that day, and eat three Shabbat meals.
All three views maintain that one should partake of three Shabbat meals, and their disagreement is only in regard to what elicits blessing and plenty for the coming week. (Or Hachamah)
This last view maintains that the Shabbat loaves are not like the show bread - it is a mitzvah to eat them, as the verse states: "….and you shall call the Shabbat 'delight'"; (Isaiah 58:13) the sages of the Talmud explain that one delights in the Shabbat with food and drink. Why should one eat all three Shabbat meals?
So that by the way of that day, delight and plenty will be found in the world….
...the Shabbat is more precious than any other time or Festival….
The Sages of the Talmud explained that the amount of a person's bread and sustenance for the entire year is set on Rosh Hashanah, the Jewish new year, excluding that which he consumes on the Shabbat or Festivals, for the more he spends to provide for those days, the more he will be given. However, since the Shabbat is the source of blessing, the more he delights in the Shabbat, the more its blessing will flow plentifully into the week ahead. This is the meaning of "by the way of that day, delight and plenty will be found in the world."
Rabbi Shimon said: Regarding one who has three meals on the Shabbat, a voice comes out and announces, "Then you shall delight in G‑d" - this refers to the first meal; "I will make you ride on the high places of the earth" - this refers to the second meal; "I will nourish you with the heritage of Jacob your father" - this refers to the third meal. For this reason, the Shabbat is more precious than any other time or Festival, for everything is found in it. This is not so at other Festival times.
Said Rabbi Chiya: For this reason, [the seventh day] is mentioned three times [here, in verses 2-3]: "With the seventh day, G‑d had completed His work;" "On the seventh day He refrained from all work;" "G‑d blessed the seventh day."
[From Zohar II, 88a; translation and commentary by Moshe Miller
First published by Fiftieth Gate Publications and Seminars.]