The Nature of the Smoke: This smoke (the cloud was like smoke) emanates from fire, but not from the fire itself, but from the substance that the fire is burning and consuming; as the earlier Possuk states: וּמַרְּאֵה כְּבוד ה' כְּאֵש אֹכֶׁלֶׁת בְּרֹאש הָהָר “The appearance of Hashem’s glory was like a consuming fire atop the mountain”. Thus, the smoke comes from the incineration and obliteration of the substance being burned.
However, regarding ‘Matan Torah’ the Torah recalls: וְּהַר סִינַי עָשַ ן כֻּלּו מִפְּנֵי אֲשֶׁר יָרַד עָלָיו הֲוָיָ' בָאֵש גו' “The entire Mount Sinai was engulfed in smoke because Hashem had descended upon it in fire”, without any mention of a ‘consuming fire’ and as the Frierdiker Rebbe points out that from the wording of the Possuk it implies that the fire itself was the cause of the smoke even though in reality smoke comes from the substance being burned and not the fire itself.
As the Frierdiker Rebbe also points out, regarding the smoke it does not matter if it is a physical fire or a fire that descends from heaven, the smoke will always only come from the substance being incinerated.
Questions on the Nature of the Miracle
Prima facie, on Mount Sinai there were neither trees, plants nor grass whose incineration would cause smoke. Furthermore, because Mount Sinai was a rocky mountain, and rocks are not combustible, what was the cause of this smoke? Additionally, The Friediker Rebbe asks about that which is stated in the Possuk: בָאֵש אֲשֶׁר יָרַד עָלָיו הֲוָיָ' ”Hashem had descended upon it in fire”. Irrespective of the intrinsic nature which Hashem had ingrained within the creation of fire, (viz. that unless there is something combustible for the fire to hold on to which causes it to remain below, it soars upwards;) here the fire descended upon the mountain irrespective of the fact that there was nothing combustible on the mountain to hold it!
The Purpose of the Miracle
The Frierdiker Rebbe explains the inner reasoning for the purpose of the creation of the world was revealed at ‘Matan Torah’. The world was created according to the laws of nature which Hashem Himself formulated, into the ‘four elements of the world’ and into the four categories of creation; the inorganic, organic, animal kingdom and mankind. According to Torah it is the job of the human to ‘transform’. Both his own nature and the nature of the world are to be transformed to make them into an abode for Hashem blessed be He. Hashem Himself initiates this process in order to teach us the possibility of change within nature.
Therefore, although Mount Sinai was a rocky, inorganic mountain, without any natural capability of incineration due to a lack of any smoke causing substances, nevertheless עָשַן כֻּלּו it became engulfed in smoke despite its non-combustible nature because אֲשֶׁר יָרַד עָלָיו הֲוָיָ' בָאֵש “Hashem descended upon the mountain in fire”, this was also contrary to the nature of fire itself whose tendency is to ascend.
