The phrase "the sons of the kingdom" is a metonym, referring to the unbelieving Jews of the kingdom of Judea. There is also irony here because the "sons" will be thrown out while the strangers will be welcomed. Alternate translation: "those who should have allowed God to rule over them" (See: [[rc://en/ta/man/jit/figs-metonymy]] and [[rc://en/ta/man/jit/figs-irony]])
Here "outer darkness" is a metonym for the place where God sends those who reject them. This is a place that is completely separated from God forever. Alternate translation: "the dark place away from God" (See: [[rc://en/ta/man/jit/figs-metonymy]])
"Grinding of teeth" here is a symbolic act, representing extreme sadness and suffering. Alternate translation: "weeping and showing their extreme suffering" (See: [[rc://en/ta/man/jit/translate-symaction]])