A readiness to pardon offenses, to overlook personal wrongs against oneself, and to harbor no desire for retaliation.
The greatest example of One who forgives is God Himself. The basis of His forgiveness is the work of Christ at Calvary. And we are unworthy objects. God could not forgive sin without proper satisfaction being made. In His love He provided the satisfaction which His righteousness demanded. In Christ, that is in His Person and work, God found a righteous basis on which He could forgive us.
Since He forgave us when we were in debt "million of dollars," we ought to forgive others when they owe us "a few dollars" (Matthew 18:23-28) JBP
Quote from Lenski :
The moment a man wrongs me I must forgive him. Then my soul is free. If I hold the wrong against him I sin against God and against him and jeopardize my forgiveness with God. Whether the man repents, makes amends, asks my pardon or not makes no difference. I have instantly forgiven him. He must face God with the wrong he has done, but that is his affair and God's and not mine save that I should help him according to Matthew 18:15, etc. But whether this succeeds or not and before this even begins, I must forgive him.
"Moreover if your brother sins against you, go and tell him his fault between you and him alone. If he hears you, you have gained your brother." NKJV
Taken from the Believer's Bible Commentary