ברא שית – בראשית, meaning created six palaces. Palaces is היכלות in plural and היכל, in singular and it has the letters of הכלי, meaning the vessel.
Supernal Mother, Binah, the seventh palace brought out six palaces. Each palace includes 7 Sefirot and so in every palace there is a palace, which is Malchut to every Sefira.
Like Binah, Malchut, which is the lower mother also brought out six that are the sky and earth. The supernal palace includes the upper three Sefirot and Yessod, which is the palace of the Sapphire stone.
Those are the six vessels that on them it said “in six days God created the heavens and the earth”.
The seventh day, Shabbat that is Malchut is taking the light from the upper three and complete the six days of creation.
Shabbat is more important than the rest of the weekdays because only in Shabbat the upper lights is revealed and spread to the rest of the week.