The Sages ask: Why does the Torah’s description of the end of the sixth day of creation conclude with “And there was evening and there was morning, the sixth day” (Bereishit 1:31), with the definite article? They explain that the Torah alludes the sixth of Sivan, when the Torah was given to Israel. “God set a condition with Creation: ‘If Israel accepts the Torah, you will continue to exist, but if not, then I will return you to being formless and void” (Shabbat 88a). Immediately after the completion of the sixth weekday was the creation of Shabbat, the expression of God’s kingship. It is upon this sixth day that, in the future, God would give the Torah to Israel (ibid. 86b).
Until Jews made their appearance in the world, Shabbat was alone, with no one present to reveal its holiness and blessedness. The Sages express this as follows:
Shabbat said before: “Master of the Universe, everybody has a partner except for me. The six days of creation pair off; only I have no partner.” God replied: “The people of Israel are your partner.” When the Jews stood before Sinai, God said to them: “Remember what I told Shabbat: ‘The people of Israel are your partner.’” This is the meaning of the commandment “Commemorate the day of Shabbat to sanctify it (Shemot 20:8).” (Bereishit Rabba 11:8)
It is true that even before the Jewish people accepted the Torah, Shabbat was already sanctified and blessed, since that is when God stopped His work. Moreover, Shabbat is the heart and soul of the world. However, the blessing that Shabbat bestowed then was limited to ensuring the world’s existence. All the imperfections endemic to the world remained, without the possibility of repair. Therefore God stipulated with His world that should the Jews refuse the Torah, the world would revert to chaos. What would be the point of its existence if it, with all its pain, were to continue without the possibility of progressing and advancing toward a more perfect state?