This is a metaphor for the fires of hell. If the term "furnace" is not known, "oven" can be used. See how you translated this in [Matthew 13:42](../13/42.md). Alternate translation: "fiery furnace" (See: [[rc://en/ta/man/translate/figs-metaphor]])
"Grinding of teeth" here is a symbolic act, representing extreme sadness and suffering. See how you translated this in [Matthew 8:12](../08/12.md). Alternate translation: weeping and expressing their extreme suffering." (See: [[rc://en/ta/man/translate/translate-symaction]])