Kalir clarified

 

Parshas שקלים The סילוק  לפרשת שקלים* starts with "אז"- "then" when Hashem created the world ------------ראית,וספרתה,והכנת,וחקרת, ומדדת, ושקלת The קליר uses 39 different words describing all the actions Hashem did to create the world. The גאון מוילנא explains the 39 words represent the 39 מלאכות that was done by Hashem to create the word. So too are the 39 מלאכות at the construction of the משכן which the Midrash compares to the creation of the world. Since כי בו שבת מכל מלאכתו  Hashem rested on Shabbos from the 39 מלאכות, so too the בני ישראל  must refrain from the 39 מלאכות on Shabbos. *The last Yotzer before the Shachris Kedusha (R. E. Hakalir)