John Gill's Exposition of the Whole Bible
Proverbs 26:21
As coals [are] to burning coals, and wood to fire,.... As brands, wood half burnt, or dead coals put to live and burning ones, soon take fire and become like them, and fit and proper fuel for them, and add to their heat:
so [is] a contentious man to kindle strife; or "a man of contentions" k; who is given to it, is full of it; it is agreeable to his natural temper and disposition; he is in his element when at it; such a man is as fuel to the fire, as a dead coal to a living one, which increases the heat of it; so does he, he kindles and spreads the flame of contention and strife.
k איש מדונים "vir contentionum", Montanus, Baynus, Piscator, Gejerus.