Parashas Vayakhel · Passuk 35:3
Torah Temimah points to classical source on this unit (verified).
English: Kindling was included among all the labors, so why was it singled out? To teach that just as kindling is a primary category for which one is liable separately, each other primary category also carries separate liability.
Derash from an item singled out from the general rule: kindling teaches חילוק מלאכות.
Kindling is singled out to establish the principle of separate liability for each primary category of Shabbos labor.