In Parshat Breisheet (Breisheet 1:31-2:1-3) we read about the completion of the creation of the world: “And God saw all that He had made, and behold it was very good. It became evening and it became morning, the sixth day. The heavens and the earth were completed, and so were their conglomerations. God completed by the seventh day His work which He had made, and He abstained on the seventh day from all His work which He had made. God blessed the seventh day and sanctified it, for on it He abstained from all His work, which God created to do.”
Did God create anything on Shabbat itself?
According to Rashi the concept of rest had not yet been created. With the coming of Shabbat came rest and when rest was created the creation was complete.
On Friday night, we recite “Vayechulu HaShamayim V’HaAretz ”, “The heavens and the earth were completed” (Breisheet 2:1-3) three times, once in the Amida (silently), once with the entire congregation in unison and once at home while reciting Kiddush over wine.
In the Talmud, Shabbat 119b, we learn from Rava or from Rabbi Yehoshua ben Levi that even if one prays as an individual on Friday night (not with a minyan) they should still recite “Vayechulu HaShamayim V’HaAretz ” as Rav Hamnuna said: Whoever prays on the eve of Shabbat and says “Vayechulu…” is treated by Scripture as if they became a partner with God in the creation…
According to Maharsha, God’s creation would have fallen short of its purpose unless people acknowledged Him as the creator.
In Breisheet Raba 10:9 we find a parable of a king who had a chupa ready, the only thing that was missing was a bride! When the world was created there was just one thing missing, Shabbat.
Each Friday evening, as we set aside our work for 25 hours and declare how God created the first Shabbat, we once again become partners in the creation of the world.