“And you (Moshe) speak to the Children of Israel saying, ‘But my Shabbos you are to observe; for it is a sign between Me and you for your generations, to know that I am Hashem Who sanctifies you” (Shemos 31:13).
The Torah makes it clear that Shabbos is not only about acting in certain ways and refraining from certain activities, it must also be a cognitive experience. Through Shabbos a Jew comes to realize and understand that G-d is the source of holiness and sanctity.
This idea is especially apparent from the laws governing the many prohibitions of Shabbos. Although there are specific labors that are forbidden on Shabbos, performing any of the forbidden labors does not automatically cause someone to be liable for desecrating Shabbos. The doer’s personal objective must be taken into account. The rule is, “מלאכת מחשבת אסרה תורה – calculated (i.e. planned) labor was forbidden by the Torah.” In other words, whether a specific labor is forbidden or not is also contingent on the forethought and motive of the doer. If the doer’s intent differs from the general motive of one who performs such labor the doer may have committed no sin at all. It all depends on the active mind.
Rav Yitzchok Hutner zt’l (Pachad Yitzchok, Shabbos, mama’ar 1:4-5) explains this concept in his characteristically profound and poignant manner:
The status of a vessel or a tool is dependent on its purpose. A small leather pouch may be used for money or to store marbles. If it is used to store money it becomes a wallet; if it is used for marbles it is a toy.
There is a prohibition on Shabbos of “hotza’ah” to transport objects from domain to domain. However, one only transgresses this prohibition if one transports an object of value. If the transported item does not possess any value, carrying it does not violate a Biblical prohibition. Therefore, transporting a vessel may not be forbidden in and of itself. It will depend on the motive of the carrier and whether there is anything in the vessel. For example, if one transports an empty silver goblet, he has transgressed the violation of carrying because the cup is his object of interest and therefore is valuable to him. However, if the goblet is filled with wine then he is not (Biblically) liable for transporting the goblet since his primary intent was to transport the wine (he is obviously liable for carrying the wine). This is true even if the goblet is more valuable than the wine. Halacha is concerned with the value of an object in regard to the specific act being performed. In regard to this specific act, the doer was not really interested in the goblet. He was only using it to facilitate the transportation of the wine which he wanted to drink along the way. Therefore, he is not liable for carrying the goblet.
This example demonstrates the concept of meleches machsheves in regard to the prohibitions of Shabbos. It is not merely the act that matters, but also the motive and intent of the doer.
Rav Hutner continues explaining that the concept of determining what is the “ikkar – priority” and what is the “tafel – accessory” is not merely one of the myriad laws regarding the prohibitions of Shabbos. Rather this concept is fundamental in regards to understanding the essence of Shabbos and the role it plays in the life of a Jew.
Chazal (Avos 5:1) explain that G-d created the physical world with “ten utterances.” Throughout the initial week of creation, utilizing those utterances G-d created, fashioned, formed, and brought forth every concept, natural law, and living being within creation. However, when the world stood completed at the conclusion of the six days, it lacked purpose and direction. It was essentially, a creation without meaning. With the onset of Shabbos, G-d invested into the world a new concept, i.e. holiness! At that point, it immediately became apparent that creating holiness was the purpose of creation. Holiness was preeminent; the rest of creation was an accessory. It suddenly became clear that the world, which until now seemed like an end unto itself, was merely a “vessel,” a conduit for holiness, and a means to reach a higher goal and purpose.