(You can read the story in Matt 18:21 - for background and combine it with Luke 17:1-6)
The question that Peter asked was actually based on the Law. What Jesus heard was: "How many times should I forgive - in order to be seen as righteous?" Jesus answered him according to the Law of the standard of God and said, "7x70, and if not you won’t qualify." He used the New Testament example of how He forgives, and said we need to be like Him, need to be as righteous as Him. Then Peter said, “Increase my faith,” thinking that we should use faith to obey the LAW, live holy and forgive, according to the impossible standard set by Jesus in order to be saved (many Christians make the same mistake). Jesus corrected the disciple and said, "It is not the amount of faith (faith to have strength to obey the law) that makes the difference but the type of faith you have." A little (small amount) of the right faith (trust in Jesus for righteousness and not our works of the LAW) will make us righteous before God.
Jesus actually explained that He is the only way to the Father and not works, even works of forgiveness. Not even our forgiveness of others can make or break that Way.