to burn: to set something alight, or to be alight, whether as a lamp that gives light or a fire that takes hold of what it touches.
This is the ordinary Greek verb for fire at work. It covers both ends of what fire does: getting a flame going, and being alight once it is. Everything else in the word's range grows out of those two.
The New Testament uses it for four kinds of burning:
- a household lamp lit and left to shine
- a mountain or a lake wrapped in flame
- dead branches thrown into a fire as fuel
- a heart set alight by words that land
More than half of the uses are about light rather than destruction. A lamp on its stand, torches burning before God's throne, John the Baptist described as a lamp that was burning and shining: in each case the burning is what makes the shining possible, and one verb does the work of both. Luke elsewhere reaches for a different verb for the striking of a light (ἅπτω), while this one covers a flame's whole life, from the moment it catches to the hours it keeps going.
The heavier uses run the other way. When Hebrews describes the mountain that blazed at Sinai, and when Revelation describes the lake of fire, this same plain verb carries the weight. The horror sits in what is on fire, not in the choice of word.
The one picture-language use is on the road to Emmaus, where two disciples say their hearts were burning while Jesus opened the Scriptures to them. The image works in English just as it does in Greek: something inside them had been lit.