From the passage in the Ten Commandments:1 “The seventh day is Shabbos to G‑d your L-rd,” our Sages2 learn that we are to refrain on that day not only from physical creative labor, but also from speaking about such labor, for just as G‑d rested from the Ten Utterances of Creation, so too are we to refrain from such speech.

Moreover, our Sages go on to say3 that on Shabbos, a pious individual shouldn’t even think about work and labor. The reason is that G‑d created with His speech the revealed world and with His thought the concealed worlds;4 just as He rested from both speech and thought on the seventh day, so too will a pious individual rest.5

Since the underlying reason for man’s cessation of creative physical labor is the same with regard to both action and speech, why is actual physical labor prohibited by the Torah, while speaking about such matters is only rabbinically proscribed, and thinking about such things is not prohibited at all, but simply not done by pious individuals?

Action differs greatly from both speech and thought, since it involves something external to the person himself. Thought and speech, however, take place within a person.

Thought reveals one’s ideas and feelings to oneself, and speech reveals them to others.6 Yet, there is a great difference between thought and speech as they relate to action:

Human thoughts are ethereal, and do not directly relate to action. Thus, one’s thoughts can only affect oneself.

Speech, however, is produced by expelling air, and requires the physical involvement of one’s tongue and lips, etc. Because it is so much closer to action, it has the power to compel others to act. Human thought, however, has no direct relationship to action.

But G‑d’s thoughts are fully capable of bringing about action, i.e., creation. The only difference between His thought and His speech is that His thought, being more sublime, creates creatures who are more spiritual, while His speech — which is on a lower level — creates revealed things.

In light of the above, it is clear that human thought cannot be compared to G‑d’s, since man’s thought alone cannot affect another’s deeds, while G‑d’s thought can and does. Man’s speech, however, inasmuch as it is capable of compelling external action, does bear some similarity to G‑d’s speech.

The factors involved in refraining from labor on Shabbos with regard to action, speech and thought can be understood accordingly:

The general reason for refraining from labor on Shabbos is, “For [in] six days, the L-rd made the heavens and the earth… and rested on the seventh day.”7 Yes, we are supposed to emulate the Creator, but although G‑d’s Shabbos rest also involved resting from speech and thought since, in man’s realm, thought and speech do not necessarily result in action, the Biblical commandment to rest on Shabbos does not require a cessation of mundane thought and speech.

Nevertheless, since there is some modicum of comparison between man’s speech and G‑d’s, our Sages — who have the power to prohibit those things that are similar to Torah prohibitions — also prohibited speaking about creative physical labor.

Man’s thoughts about labor, however, can in no way compare to Divine thought, so there is no reason for it to be even rabbinically prohibited. Still, a pious individual who seeks to emulate G‑d’s ways will refrain from mundane thoughts on Shabbos, since G‑d rested on the seventh day from thoughts of creation.

Based on Likkutei Sichos, Vol. XI, pp. 80-85