Tafsir of Ghafir 40:41

[He] repeated their address to awaken them from the slumber of heedlessness, to emphasize the importance of the one being addressed, and to exaggerate in rebuking them for how they responded to his invitation. The conjunction was omitted in the second address—"And O my people! The life of this world is but a temporary enjoyment," etc.—because it serves as an explanation for what was generalized in the address before it, regarding the guidance to the path of rectitude; for that guidance is the warning against clinging to this world and the encouragement to prefer the Hereafter over the former. He performed that in the best and most perfect manner.

It was not omitted in this [third] address because it does not hold the same status. This is because it is for the purpose of weighing the two invitations: his invitation to the religion of Allah, the fruit of which is salvation, and their invitation to take partners [with Allah], the consequence of which is the Fire. This is in no way an explanation of the guidance; rather, it is to establish that he is a guide and they are misguiders, and that what he is upon is guidance and what they are upon is misguidance. Thus, it is a conjunction to the first address, or to the whole. It has also been said: It is a conjunction to the second address, included with it in the explanation of what was generalized in the first address, both explicitly and implicitly. For every view, there is discussion regarding its preference.