Nombres 28:9

but on the day of Shabbatha two lambs of the year without blemish, and two-tenths of flour mixed with olive oil for the mincha and its libation.

וביום השבת, “and on the Sabbath day, etc.;” there is a comment by Midrash Shocher tov on Psalms 92,1 that amongst all the mussaph offerings there is none that is as inexpensive as that of the Sabbath, i.e. consisting of only two not more than one year old sheep. According to the author of that Midrash the Sabbath complained to G–d about this. G–d told the Sabbath that this day is distinguished by a number of things that occur on it or relating to it in duplicates. It has two hymns dedicated to it; its special offering consists of two sheep; it is known as עונג, “pleasure, delight,” not once but twice; when it is deliberately desecrated it brings a dual penalty, i.e. מות יומת, the show breads are paired on the table in the Temple. This is also why we speak of this mussaph offering being כראוי, “tailored to its essence.” This is an expression that has not been applied to the mussaph offerings on any other occasion. The Midrash elaborates by means of a parable: a King told his servants to prepare his meal for “my sons”. The servants prepared two separate meals. After both his sons had consumed these meals, the king asked for a meal to be prepared for him. The servants asked him which kind of meal he desired. The king asked what kind of meal they had served to his sons? The servants spelled out the details for him. The king then responded that they should not prepare a more elaborate meal for him than they had prepared for his sons. [My version of this Midrash does not quote the Sabbath as having complained to G–d. Ed.]
G–d acted in a similar manner when He provided the Jewish people with a double portion of manna for the Sabbath even before the Sabbath had commenced. Seeing He gave His people the equivalent of two loaves of bread before the Sabbath, He wished this to be remembered by “feeding” Him the equivalent of two loaves of bread as the special offering on the Sabbath. This is what the two sheep of the mussaph offering on that day represent. Seeing that we are on the subject of preparations for the Sabbath, let us explain also the central part of the Sabbath Mussaph prayer which commences with the words: תכנת שבת, “You (G–d) have instituted the Sabbath, etc.” The sequence of the letters תכן in the word תכנת, are a reminder of Exodus 5,18, where in response to Moses requesting a three day vacation for the Israelites to serve the G–d of his people, Pharaoh not only refused, but doubled the work load of the people by denying them the straw that had been given to them for making bricks, and insisting that the daily number of bricks required תכן לבנים, remain the same. The “institution” the author of the prayer speaks of refers to G–d having named each day of the creation sequentially so that the Sabbath would be the seventh day, a number which G–d is especially fond of. (Compare Vayikra Rabbah 29,11) [The author of the Midrash there makes a long list of proving the statement he has just made. Ed.] He claims that this is why G–d took a special liking to Chanoch, the outstanding human specimen of the seventh generation.]