Prior to this, Jesus has been telling his disciples to forgive each other. The conversation goes something like this:
Jesus: Forgive a lot. In fact, forgive everyone everything.
Disciples: Gosh, that's hard. We need more faith to do that! Give us more faith!
Jesus: You don't need more. You just need some. And you obviously don't have any.
Next Jesus tells them a parable about how improper it would be for a servant to return from the fields and expect his master to reward him for his work. The servant's work is just what's expected of him. It's what the servant owes his master. When the servant returns from the fields, he serves his master, continuing to put the master's desires above his own. That is the proper order of things. End of story.
I think Jesus is telling his disciples that forgiving others isn't some sort of unreasonable request from God. It's just what we owe our master. Not only that, but we don't need an extra portion of faith to do this. Forgiving others for the things they do against us—even if they do it seven times a day—can be done with the smallest portion of faith imaginable.
This means that the WWII Christian-Jews who forgave their German captors weren't some sort of super-Christians. They were just doing their duty to God.
This also means that when Stephen in Acts 7 asked God not to hold his murderers' sin—the stoning of himself—against them, he hasn't reached some unattainable level of holiness. He was just operating on a mustard-seed amount of faith.
This also means that my seemingly insurmountable troubles, relationships, and fears are not places where I need more faith, but rather, places where I have no faith at all. Faith doesn't come in degrees. Either we trust the Lord in a particular area or we don't. There's no such thing as sorta trusting in the Lord.
I suppose this might seem confusing because our lives progress. Our lives are like this path that unrolls in front of us, and along the way we get to see if our faith works at different times and at different places and with different people. This is the working out of our salvation or the kingdom of heaven being worked into our life. When we encounter new circumstances, we get to find out if our faith is going to work here too.
Do I still believe that Christ has already made me good even when I can't seem to meet all the demands being made on me?
Do I still believe the God loves to hear my requests even when others' needs seem so much more important than mine?
Do I still believe that God wants me, even if I can't tie a pretty ribbon onto the end of each project or a happy ending onto the end of every relationship?
Do I still believe that Jesus has experienced all that I'm feeling even when those closest to me seem tired of listening to me?
Do I still believe that a personal relationship with Jesus is enough to say yes even when I don't understand how exactly I will interact in this new activity?
Do I still believe that God knows my future and that what happens will be for my good even when I can imagine a dozen ways that this can all go wrong?
Do I still believe that God is the ultimate comforter to me when I decide to look a problem full in the face even when I can't see how examining this problem will come to any good?
Do I still believe that God's power is behind every authority on earth even when the government tells me to do things I don't want to do?
Do I still believe that the Holy Spirit wants to move me into action even when that action could disrupt others or myself?
Do I believe that with Christ in me and through me and around me all these things are as simple to do as it was for the Lord God to speak trees and oceans into existence?