Matthew 18:35 That is what my Father in heaven will do to you if each of you does not sincerely forgive other believers."
Jesus had given the procedure for dealing with a believer who sins against another believer and when He was done, Peter asked, “how often do I have to forgive a believer who wrongs me? Seven times?" Jesus replied by saying, “I tell you, not just seven times, but seventy times seven.” Jesus then told a story to illustrate what happens when we don't forgive. He starts the story by saying, “Therefore the kingdom of Heaven has been compared to a certain king who desired to make an accounting with his servants.” Some translations start with “Because of this...” or “That is why...” All of Matthew 18:35 is dealing with an church member who had done wrong and this part of the chapter is on forgiving that church member. So Jesus is saying this is how God will deal with those who are in a position to forgive another.
The story Jesus tells is about a king who is wanting to settle accounts with his servants. The king discovered one of his servants owed him 10 thousand talents. One talent was the same as 6,000 denarii, so the servant owed the king 60,000,000 denarii. Keep that in mind. That piece of information will become more important later in the story. The servant was unable to pay the debt so the king ordered for the man, his wife, his children, and all they owed, to be sold. The servant fell to the king's feet, begged the king to be patient, and promised he would pay off the debt. The king felt compassion for the man and canceled the debt. Imagine the relief the servant felt knowing he and his family wouldn't be sold, and the whole debt was removed. This man never had to worry about it again.
The servant went away and found one of his fellow servants who owed him 100 denarii. He grabbed that servant by the throat and began to choke him. He said, “Pay what you owe me.” The fellow servant fell to his feet, begged him to be patient, and promised to pay off the debt. But the servant refused and ordered the fellow servant to be put in prison until he could pay off the debt. Other servants saw what had happened and told the king. The king ordered the servant to come back and said to him, “You wicked servant! I forgave you all that debt because you begged me. Should you not also have had compassion on your fellow servant, as I also had compassion on you?” Then the king handed the servant over to his tormentors until he could pay off the debt. In other words, the servant was punished for not forgiving his fellow servant when he had just earlier begged for, and received, forgiveness from the king. Jesus ends the story by saying, “That is what my Father in heaven will do to you if each of you does not sincerely forgive other believers."
When a person repents, we have a duty to honestly and fully forgive them. There should be no hard feelings, no grudges, no reminding the person of their error at some later date. There should be no mention of it to the person or to anyone else ever again. It is now in the past and done with. Leave it alone. If there are any doubts as to how important this is, read the following texts:
"If you forgive the failures of others, your heavenly Father will also forgive you. But if you don't forgive others, your Father will not forgive your failures.” Matthew 6:14-15
“Whenever you pray, forgive anything you have against anyone. Then your Father in heaven will forgive your failures.” Mark 25:5
“Be merciful just as your Father is merciful. Do not judge others, and God will not judge you; do not condemn others, and God will not condemn you; forgive others, and God will forgive you.”
Luke 6:36-37
All of us are in need of God's forgiveness. We easily talk about God's forgiveness and expect to be forgiven, but we don't often extend that same forgiveness to each other. When we let go of our anger, hatred, and grudges, and forgive others we can then claim this beautiful promise;
“If we confess our sins, He is faithful and righteous that He may forgive us the sins, and may cleanse us from all unrighteousness.” 1John 1:9