Mishkan, Melachot, Shabbat

The Baal HaTurim at the beginning of the parsha says לעשות – אותיות ל׳ תשע וחסר וי״ו לומר ל״ט מלאכות נעשה אותם בו׳ ימים ולא בשבת וכן אשר ברא אלהים לעשות הכתוב בויכולו תמצא עשיות ובריאות ומלאכות והויות והוצאות והבדלות כולם ל״ט לומר ל״ט מלאכות הן חוץ לתולדותיהם וכן תמצא מויקהל עד לא תבערו וגו׳ ביום השבת ל״ט תיבות חוץ ממלת השבת.  Chazal derive the 39 melachot from the words לעשות אותם.  Why are the 39 melachot derived from the parsha of Shabbat here and not from the earlier parshiot?  Why are the melachot prohibited the same as the 39 activities done in the Mishkan?  

The Tikkunay Zohar (#48) says the 29 melachot of Shabbat correspond to 39 curses that were given after the sin of Adam.  The Sifsay Chayim (Moadim volume 3 on Shabbat and Mikdash ) explains that before the sin, Adam didn't need to do anything to perfect the impurities in the world, only after the sin the impurities were brought into the world and Adam has to perfect it by working the world.  The melachot of Shabbat correspond to the work that must be done to remove the impurities that exist in the world.  On Shabbat, we are able to access a bit of the level of Adam before the sin and hence we abstain from the melachot which are used post sin.  

The Be'ar Moshe says that we can understand that is why the 39 melachot are mentioned only here.  Before the sin of the agel, there was a chance to correct the sin of Adam and then there would be no need for the 39 melachot ever.  Only after the sin of the agel that was such a possibility lost and now the 39 melachot become necessary during the week do they become prohibited on Shabbat when we taste a level of Adam pre sin.  

Why is Shabbat here called שבת שבתון?  The pessukim flow as אלה הדברים, these are the 39 forbidden melachot now that you need to fix the world.  Therefore, you shall work six days, if you work on those days it order to perfect the world, שבת שבתון, not only will Shabbat be holy but the week will also be elevated, שבת שבתון, the kedusha of Shabbat will spread to the entirety of the week (see ישמח משה עד"ז.)