שמות לה:ב פירוש: רש״י, ספורנו, אור החיים וטור הארוך

ששת ימים SIX DAYS [MAY WORK BE DONE] — He intentionally mentioned to them the prohibition in reference to the Sabbath before the command about the building of the Tabernacle in order to intimate that it does not set aside (supersede) the Sabbath (cf. Mekhilta d'Rabbi Yishmael 35:1:1).

וביום השביעי יהיה לכם קדש, and you may not violate the Sabbath even in order to complete the Tabernacle sooner, although the work on the Tabernacle is also a sacred task.

ששת ימים תעשה מלאכה, "during six days work shall be performed, etc." The reason the Torah emphasises the work to be performed on the weekdays may simply be a hint that if one observes the seventh day as a holy day, the work required for our maintaining ourselves during the subsequent six days will take care of itself.