Remember the context; Jesus has been telling the disciples how to deal with another Christian who has sinned against them.
Peter wants to know how many times he has to forgive someone, seven?
Jesus says seventy times seven. Sounds like He is saying “EVERY time” to me.
Then He tells of a man who owed his master more than could be repaid in many, many lifetimes. He begged time to repay and was completely forgiven. This is representative of us – our sins create a debt that we could never repay, and when we accept Christ and seek forgiveness we are completely forgiven.
Hopefully we are not ungrateful like the man Jesus tells us about. Jesus says that if we want to be forgiven that we must in turn forgive our brother (or sister).