Is it “fair” that we should be forgiven of our sins through faith? Certainly it represents infinitely grace beyond what we deserve. A Christian who truly understands the extent of their sin and the completeness of their forgiveness because of the atoning death of Jesus should show others grace too.
Here’s a parable from Matthew 18 that illustrates the point:-
The Parable of the Unforgiving Servant
21Then Peter came to Him and said, “Lord, how often shall my brother sin against me, and I forgive him? Up to seven times?”
22Jesus said to him, “I do not say to you, up to seven times, but up to seventy times seven. 23Therefore the kingdom of heaven is like a certain king who wanted to settle accounts with his servants. 24And when he had begun to settle accounts, one was brought to him who owed him ten thousand talents. 25But as he was not able to pay, his master commanded that he be sold, with his wife and children and all that he had, and that payment be made. 26The servant therefore fell down before him, saying, ‘Master, have patience with me, and I will pay you all.’ 27Then the master of that servant was moved with compassion, released him, and forgave him the debt.
28“But that servant went out and found one of his fellow servants who owed him a hundred denarii; and he laid hands on him and took him by the throat, saying, ‘Pay me what you owe!’ 29So his fellow servant fell down [e]at his feet and begged him, saying, ‘Have patience with me, and I will pay you [f]all.’ 30And he would not, but went and threw him into prison till he should pay the debt. 31So when his fellow servants saw what had been done, they were very grieved, and came and told their master all that had been done. 32Then his master, after he had called him, said to him, ‘You wicked servant! I forgave you all that debt because you begged me. 33Should you not also have had compassion on your fellow servant, just as I had pity on you?’ 34And his master was angry, and delivered him to the torturers until he should pay all that was due to him.
35“So My heavenly Father also will do to you if each of you, from his heart, does not forgive his brother [g]his trespasses.”