When Jesus talks about “little ones” here it seems that He is talking about those who are young in faith, not necessarily young in age. We are to be careful how we live, because the way we live influences others. We should stay away from sin, but we should also understand how easy it is to sin, and be willing to forgive others when they sin against us. It’s also very important that we understand how big a part repentance plays in our relationships with others. If someone has wronged us, then we should do everything in our power to not be spiteful, resentful, or angry towards them, even though our relationship may not be the same. However if they express repentance, then we are obligated to forgive and restore (17:1-4). How do we know if the repentance is real? Only time will tell, and if we consistently deal with someone who expresses false repentance, then the relationship may never be fully restored, but we still should make sure that we don’t live in a constant state of bitterness and anger towards them.
So, shouldn’t we be moving mountains with the faith we have?!?!? I think that Jesus’ point here is that we use the faith we have. If we express our faith in service and obedience, then our faith will naturally grow (17:5-6). And we see that emphasis on duty and service in His next words. We don’t demand things from God, we serve Him, and we recognize that the greatest gift is knowing Him and serving in His kingdom (17:7-10). In fact, rather than seeking praise from Him for doing our duty, we should be expressing thanks to Him for everything He’s done for us (17:11-19)! And we again see Jesus throw in a detail to make everyone think. Did you catch that the grateful leper was a Samaritan?!?!? How do you think people responded to that?