Parshas Vayakhel opens with Moshe Rabbeinu reiterating the mitzvah of abstaining from melachah on Shabbos. Immediately thereafter, Moshe Rabbeinu communicates to the entire Jewish people the mitzvah of building the mishkan. This juxtaposition of mitzvos Shabbos and the mishkan provides the foundation for much of hilchos Shabbos. This juxtaposition, according to Chazal, teaches that the 39 forms of melachah needed for the mishkan constitute melachah on Shabbos, and accordingly are prohibited.
Primo facie, this derivation is most paradoxical. The melachas performed for the sake of the mishkan are sources of kedusha; how can these very same melachas serve as the standard for profaning kedushas Shabbos?
In order to recognize the answer to this question, we must reverse our perspective on the relationship between Shabbos and the mishkan. In terms of derivation, the issur melachah on Shabbos is defined by melachas of the mishkan. The correct conceptual relationship, however, is that these activities from which we abstain on Shabbos (i.e., the 39 melachas) accordingly become capable of generating kedusha. It is precisely because we abstain from the 39 melachas on Shabbos that we can utilize them to create kedusha during the sheishes yemei hama'aseh.
The wellspring for human creativity in the realm of kedusha is Shabbos. Our embrace of kedushas Shabbos which involves withdrawal from worldly pursuits and signifies recognition of HASHEM's sovereignty and our own absolute dependence upon Him enables us to create kedusha. Our rendezvous on Shabbos with HASHEM who is the source of kedusha allows us to create kedusha.