Matthew 18:32-33 Then his lord, after that he had called him, said unto him, O thou wicked servant, I forgave thee all that debt, because thou desiredst me:
33 Shouldest not thou also have had compassion on thy fellowservant, even as I had pity on thee?
Third person reciprocity became better known through the movie Pay It Forward which was based on a book of the same name. The movie poster has this sentence, “When someone does you a big favor, don’t pay it back… pay it forward.” This is third person reciprocity put in more simple terms.
Reciprocity in general is an ancient economic system. Simply put it means if someone does something for you then you are obligated to do something equally valuable for them. If a wheat farmer needs fruit he will give a fruit farmer wheat after harvest expecting the fruit farmer to reciprocate with an equal value of fruit after the fruit is harvested.
In the case of third person reciprocity the wheat farmer would freely give his wheat to the fruit farmer as a gift to help the fruit farmer. The fruit farmer would then give fruit to someone else who needed help. There is an understood obligation to help others when someone has helped us.
This is the teaching in the passage above. Read the story surrounding these verses and remember that this is Jesus' illustration of the Christian practice of third person reciprocity. We are obligated to give what Jesus has so freely given to us to others who are in need as we once were.
In a broader sense third person reciprocity is required of all people by God, because He has showered us all with His gifts of grace. This teaching is not just in the New Testament, it is all through the Bible. Deuteronomy 24:17-22 and Exodus 22:21-27 detail this requirement in the Mosaic Covenant. We who have received benefit from God in the past, even in our ancestors, must return the same to people in our present who are in need of it.