Rashi on Exodus 31:13/רש"י על שמות ל״א:י״ג

1ואתה דבר אל בני ישראל SPEAK THOU ALSO UNTO THE CHILDREN OF ISRAEL — AND thou, although I have given thee charge to command them concerning the work of the Tabernacle let it not appear a light thing to thee to set the Sabbath aside on account of that work.

2אך את שבתתי תשמרו BUT NEVERTHELESS MY SABBATHS SHALL YE KEEP — Even though you be anxious and alert to do the work promptly the Sabbath nevertheless you must not set aside on its account. The words אך and רק wherever they occur in Scripture have limitative force (Rosh Hashanah 17b; cf. Rashi on Rosh Hashanah 17b on אכין ורקין). Here Scripture intends by the word אך to except the Sabbath from the days on which the work of the Tabernacle may be done.

3כי אות היא ביני וביניכם FOR IT IS A SIGN BETWEEN ME AND YOU — There is a mark of distinction in the relation that exists between us, viz., the fact that I have chosen you by letting you inherit for rest that day on which “I” rested.

4לדעת TO KNOW — (not, “for you to know”, but) for the nations of the world to know through it, כי אני ה' מקדשכם THAT I AM THE LORD THAT DOTH SANCTIFY YOU.