The second mishna in the first chapter of the tractate Shabbos states that one should not enter one’s tannery (shop that treats animal skins) before shabbat on friday afternoon. This command is said in the context of other items not to be done on Friday before Shabbat.
The Gemara states that one must be not enter his tannery because one might find a skin which is damages. Rashi adds that if one enters his shop and and finds the damaged item it will disturb not only his shabbat, but also his disturb his ability to pray.
A rashi in the Torah already advises that when it comes to Friday, one should view his work as all completed.
The lesson is clear. Shabbos teaches a Jew values of priority. Work is certainly important. But there comes a time when one must put aside his physical pursuits and focus his mind on spiritual values and pursuits. The Shikker Dovid would like to emphasize that working and plugging away is meaningless, unless it is coupled with a value system that includes spiritual pursuits. True peace of mind will come, when we spiritually elevate ourselves to learn this value.