Our Scripture reading today is 2 Corinthians 2:5-11.
Verse 10, "To whom ye forgive any thing, I forgive also: for if I forgave any thing, to whom I forgave it, for your sakes forgave I it in the person of Christ;"
We are setting ourselves up for being taken advantage of by our enemy when we refuse to forgive.  Satan is very powerful and does not need our help in gaining any advantage over us.  Forgiveness has been given to each of us time and time again.  God sets the example for us to follow.  If the creator God forgives sinners like you and me, why are we unable to forgive other sinners?  
The key to forgiveness is really the key to having victory in every area of the Christian life.  It is impossible to forgive in the power of the flesh.  Paul said it best at the end of verse 10.  He forgave in the "person of Christ."  When Jesus said we could nothing without Him, it included forgiving someone.  There is no grievance too difficult to forgive if we are walking in the Spirit. Galatians 5:25, "If we live in the Spirit, let us also walk in the Spirit."  It has been said that we are most like Jesus Christ when we are willing to forgive.  It also keeps the advantages of our enemy as low as possible.