Driving a Donkey and Melachah
The Gemara here teaches us that although it is forbidden to drive a donkey (mechamer) or work any other animal on Shabbos, a person who does so deliberately is not subject to the death penalty, nor is a person who drives his donkey in error subject to an obligation to bring a chatas sin-offering. Thus, mechamer differs from the thirty-nine melachos, which are subject to these penalties. Moreover, although the person who deliberately drives his donkey on Shabbos is in deliberate violation of a prohibition, he is not subject to the penalty of lashes generally imposed on those who violate Torah prohibitions. [Rambam (Hil. Shabbos 20:1) explains that this is because the prohibition to drive a donkey is derived from the positive command to allow animals to rest on Shabbos (Shemos 23:12), and there are no lashes for a prohibition that is derived from a positive command ( לאו הבא מכלל עשה אין לוקין עליו ) — see the next law there (20:2) for the reason why the general negative command that forbids working one’s animal together with all forms of forbidden melachah on Shabbos (Shemos 20:10) does not generate the penalty of lashes (taken from the Gemara here, 154a-b).]
On the basis of our Gemara, Meshech Chochmah (to Bamidbar 4:3) explains an interesting discrepancy in the Torah’s language. In that pasuk, which describes the recruitment of the Levite family of Kehas we read: כָּל־בָּא לַצָּבָא לַֽעֲשׂוֹת מְלָאכָה בְּאֹהֶל מוֹעֵֽד — the word melachah appears. However, concerning the tasks of the family of Gershon we read (ibid. 4:24): זֹאת עֲבֹדַת מִשְׁפְּחֹת הַגֵּֽרְשֻׁנִּי לַֽעֲבֹד וּלְמַשָּֽׂא , and concerning the tasks of the family of Merari we read (ibid. 4:31): וְזֹאת מִשְׁמֶרֶת מַשָּׂאָם לְכָל־עֲבֹֽדָתָם בְּאֹהֶל מוֹעֵד . In both these places the word melachah does not appear.
Meshech Chochmah notes that the family of Kehas was required to physically carry the items from the Mishkan for which they were responsible, while the families of Gershon and Merari placed the items that were their responsibilities on carts that were led by oxen. Hence, if the task of the family of Kehas would have been performed on Shabbos, it would constitute a violation of the melachah of hotzo’oh; while the tasks of Gershon and Merari would constitute a violation of mechamer. Since only hotzo’oh can be categorized as a melachah, the Torah only used the word melachah in conjunction with the tasks of the family of Kehas.