They say that lightning is Brahman, because lightning (vidyut) is called so from cutting off (vidanat). Whosoever knows this, that lightning is Brahman, him (that Brahman) cuts off from evil, for lightning indeed is Brahman.

In plain words: People say lightning is Brahman, the ultimate reality, because the word for lightning comes from the idea of 'cutting.' Whoever knows this is cut free from evil by Brahman.