On the matter of observing Shabbat in the work, since there are six days of action, which are weekdays, and there is Shabbat, when it is forbidden to work, “weekday” means when a person feels that he is far from Kedusha [holiness]. At that time, he has the work of correcting his practices so as to bring himself closer to Kedusha. Kedusha means that he has equivalence of form. Then, to the extent that he draws closer, he feels the abundance of Kedusha.
Naturally, when he comes to feel the Kedusha, he has no work in correcting the evil. This is why at that time it is called Shabbat, since he Shavat [ceased/rested] from all his work. This means that only when one is in the weekdays, when he does not feel the Kedusha, there is work in correcting the evil.
Hence, the work of the weekdays is called an “awakening from below,” and on this comes an awakening from above called Shabbat, when the Kedusha is poured upon him by the Creator. At that time, one should observe the Shabbat, meaning that all his work is to observe the Shabbat—not to distract his mind from the Kedusha of the Shabbat.
In the matter of observing, its importance becomes clear. There is a rule in nature that the more something is important, the better guard it needs. Likewise, the less something is important, its keeping is also not as much. Hence, the work of observing Shabbat is expressed in the greatness and importance of the Kedusha of the Shabbat.
This brings up the question, How can one come to feel the importance of Kedusha? The answer is that it comes from the work during the weekdays. To the extent that he regrets during the weekdays that they are regular days and not holy days, to that extent he values the Shabbat, as it is written, “Anyone who observes the Shabbat properly, desecrates it.” That is, the fact that he can observe the Shabbat properly depends on his secularity, namely on his work during the weekdays.