Fret... — This verb, repeated in Psalms 37:7-8, is found besides only in Proverbs 24:19. Its meaning is to heat or inflame oneself.
Neither be thou envious... — This has a similar root-meaning (comp. our “burn with jealousy”), and so is in close parallelism with “fret.” This verse occurs almost word for word in Proverbs 3:31; Proverbs 23:16; Proverbs 24:1. and Psalms 73:3.