Matthew 6:15
15 But if ye forgive not men their trespasses, neither will your Father forgive your trespasses.
In this life, its about how we deal with an offense, which is the point of bing Christ like.
Luke 6:29-30
29 And unto him that smiteth thee on the one cheek offer also the other; and him that taketh away thy cloak forbid not to take thy coat also.
30 Give to every man that asketh of thee; and of him that taketh away thy goods ask them not again.
This does not mean we are to be door mats, but that we seek peace, and have a forgiving spirit. In this regard when we are hurt or offended, we should not look to those who have hurt and offended us with regard to the offense, rather we look at how we dealt with the offense.
Do I curse them back, get violent, become vengeful etc, or can you instantly forgive them? When a person offends you the judgment is also on them for what they have done to you. God remembers and will look out for you…
Luke 17:1-2
1 Then said he unto the disciples, It is impossible but that offences will come: but woe unto him, through whom they come!
2 It were better for him that a millstone were hanged about his neck, and he cast into the sea, than that he should offend one of these little ones.
Matthew 18:6
6 But whoso shall offend one of these little ones which believe in me, it were better for him that a millstone were hanged about his neck, and that he were drowned in the depth of the sea.
The first thing I would do is forgive them in your heart, then write the letter asking them to forgive you for the way you have felt towards them as a result of their offense. This sets the stage for the Lord to forgive you for anything you have done against the Lord word.
Forgiveness is NEVER about the person your forgiving, its about your freedom and relationship with God. The longer you harbor unforgiveness, you are not forgiven the things you do. More accurately, it is being cut off from God, He will not hear anything you have to say, until you forgive others. In that regard forgiveness is about you.
Jesus said it this way..
Matthew 18:21-35
21 Then came Peter to him, and said, Lord, how oft shall my brother sin against me, and I forgive him? till seven times?
22 Jesus saith unto him, I say not unto thee, Until seven times: but, Until seventy times seven.
23 Therefore is the kingdom of heaven likened unto a certain king, which would take account of his servants.
24 And when he had begun to reckon, one was brought unto him, which owed him ten thousand talents.
25 But forasmuch as he had not to pay, his lord commanded him to be sold, and his wife, and children, and all that he had, and payment to be made.
26 The servant therefore fell down, and worshipped him, saying, Lord, have patience with me, and I will pay thee all.
27 Then the lord of that servant was moved with compassion, and loosed him, and forgave him the debt.
28 But the same servant went out, and found one of his fellowservants, which owed him an hundred pence: and he laid hands on him, and took him by the throat, saying, Pay me that thou owest.
29 And his fellowservant fell down at his feet, and besought him, saying, Have patience with me, and I will pay thee all.
30 And he would not: but went and cast him into prison, till he should pay the debt.
31 So when his fellowservants saw what was done, they were very sorry, and came and told unto their lord all that was done.
32 Then his lord, after that he had called him, said unto him, O thou wicked servant, I forgave thee all that debt, because thou desiredst me:
33 Shouldest not thou also have had compassion on thy fellowservant, even as I had pity on thee?
34 And his lord was wroth, and delivered him to the tormentors, till he should pay all that was due unto him.
35 So likewise shall my heavenly Father do also unto you, if ye from your hearts forgive not every one his brother their trespasses.
If you write a letter about your forgiveness, it will turn into a criticism letter because you will vent your hurt.
Asking them to forgive you will convict them of their own behavior and remove any initial awkwardness over the hurt.
Next, be prepared to be gracious.