This verse is in a real sense the key to the entire parable: those persons whose debt of sin God has forgiven are obligated in return to forgive the sins that others commit against them.

And should not you have…? is more literally “and was it not necessary for you to have…?” Since this type of structure is extremely difficult for English speakers, Good News Translation has made three adjustments in hopes of relieving the difficulty: (1) the rhetorical question is changed to a statement; (2) the negative form is altered to a positive; and (3) the impersonal structure (“was it not necessary for you”) is made into a second person form (“You should have had mercy”). The verb translated should … have (literally “it was necessary”) normally indicates a binding compulsion or obligation; see, for example, its usage in Luke 2.49; 15.32; 18.1; Acts 5.29; 1 Thessalonians 4.1; Titus 1.11.

In other languages it has still been possible to retain a question in rendering the sentence, as for example in “And so what should you have done? You should have had mercy on your fellow servant just as I had mercy on you.” Another example is “You should have had mercy on your fellow servant as I did on you, shouldn’t you?”

That the verb had mercy on is used twice in this verse emphasizes the importance attached to it. For some languages the two clauses may more naturally be reversed: “I had mercy on you, and that is why you should have had mercy on your fellow servant.”

Quoted with permission from Newman, Barclay M. and Stine, Philip C. A Handbook on the Gospel of Matthew. (UBS Handbook Series). New York: UBS, 1988. For this and other handbooks for translators see here .