# sons of the kingdom will be cast out

"God will throw the sons of the kingdom out"

# the sons of the kingdom

The phrase "the sons of the kingdom" refers  to people who belonged to the  kingdom. Alternate translation: "the citizens of the kingdom"or "those who should have allowed God to rule over them" 

# the outer darkness

Here "outer darkness" is the place where God sends those who reject them. Alternate translation: "the distant dark place"

# weeping and grinding of teeth

"Grinding of teeth" here is a symbolic act, representing extreme sadness and suffering. Alternate translation: "weeping and showing their extreme suffering"