The picture is that of fastening a firebrand to oneself, in order to free one’s hands while walking in the dark. This sounds very dangerous. Perhaps the idea is that those who refuse the only true light in favour of embracing another, manmade light (that is, an earthly resource) actually open themselves to being devoured by the flame.1
11 Behold, all you who kindle a fire, who equip yourselves with burning torches! Walk by the light of your fire, and by the torches that you have kindled! This you have from my hand: you shall lie down in torment.