There is a Misva to personally involve oneself in some aspect of the Shabbat preparations. Even a person who has hired help for the preparations should reserve some task for himself. It is preferable to purchase food for Shabbat on Friday, and not earlier, unless there would not be enough time to finish the preparation by the onset of Shabbat. One should bake Halot for Shabbat, and this should be done on Friday, and not earlier, since the Misva of separating Hala from the dough serves to atone for Hava’s sin, which took place on Friday.
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Adopted from the shiurim of Ha Rav Eli J. Mansour