Jesus was very explicit in seeing to it that we understand the danger of harboring unforgiveness. After reading this parable, there should be no question of the consequences of having an offense in your heart:

Therefore is the kingdom of heaven likened unto a certain king, which would take account of his servants. And when he had begun to reckon, one was brought unto him, which owed him ten thousand talents.

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. The servant therefore fell down, and worshipped him, saying, Lord, have patience with me, and I will pay thee all.

Then the lord of that servant was moved with compassion, and loosed him, and forgave him the debt. 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, and then said, Pay me what thou owest.

And his fellowservant fell down at his feet, and besought him, saying, Have patience with me, and I will pay thee all. And he would not: but went and cast him into prison, till he should pay the debt.

So when his fellowservants saw what was done, they were very sorry, and came and told unto their lord all that was done. 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:

Shouldest not thou also have had compassion on thy fellowservant, even as I had pity on thee? And his lord was wroth, and delivered him to the tormentors, till he should pay all that was due unto him.

So likewise shall my heavenly Father do also unto you, if ye from your hearts forgive not every one his brother their trespasses.
(Matt. 18:23-35)

No matter how great the hurt or the offense, if we don't freely forgive from the heart, we will be turned over to the tormentors. This is just as clear as the nose on our face.

We can go to church, pay our tithes, go to prayer meetings, and we can preach and declare the Word of God, but if we continue to hold and harbor offense in our hearts, the Word says,

So also My heavenly Father will deal with every one of you if you do not freely forgive your brother from your heart his offenses.
(Matt. 18:35 AMP)

Do you understand how deadly it is to hold offenses in your heart? You're doing no one any good, only hurting yourself and possibly your eternity. If you do not freely forgive from the heart, then Jesus cannot forgive you. It's the Word. This is scripture. I didn't write it.

I'm endeavoring, to the best of my ability, to get this over to you as seriously as the Lord got it over to me. He said to me, "Carolyn, you cannot be forgiven if you cannot forgive. You're going to have to pay the original unpayable debt."

Haven't you carried certain things around with you long enough? The Lord wants you free of it all. He wants you totally and completely free!

For verily I say unto you that whosoever shall say unto this mountain, Be thou removed, and be thou cast into the sea; and shall not doubt in his heart, but shall believe that those things which he saith shall come to pass; he shall have whatsoever he saith.

Therefore I say unto you, What things soever ye desire, when ye pray, believe that ye receive them, and ye shall have them.

And when ye stand praying, forgive, if ye have aught against any: that your Father also which is in heaven may forgive you your trespasses.

But if ye do not forgive, neither will your Father which is in heaven forgive your trespasses.
(Mark 11:23-26)

It's clear Jesus meant what He said.

For if ye forgive men their trespasses, your heavenly Father will also forgive you: But if ye forgive not men their trespasses, neither will your Father forgive your trespasses.
(Matt. 6:14-15)

Forgive and ye shall be forgiven.
(Luke 6:37)

Forgiveness is a debt we owe, but when you forgive, it cancels that debt and frees you from the shackles of offense. For us to be free and receive from God, we must forgive.

Source: Conquering The Spirit Of Offense by Carolyn Savelle.
Excerpt permission granted by Jerry Savelle Publications