Think of a man who keeps an account of money others have borrowed from him and he is occupied with finding ways of extracting those amounts from them with interest. Now think of what goes on in our mind when we think of people who have done us wrong in the past. Are we agitating over how we can get back at them, how we want God to make them bleed for it till the last drop, how we can expose them so that everyone will know the truth, how we can confront them and make them fall cowering at our feet, etc.? We may think that we are only being righteous and fair and that they deserve all this and more. But righteousness and justice are not the only things we are to consider.
To understand this, think of where we stand before God. This holy God is so perfectly righteous, holy and just that it would be totally fair for Him to send us straight to hell for the sins we have done (Ro.6:23a). That is what we deserve. But He has been gracious to us, not counting our sins against us but crediting the righteousness of Christ into our account when we repented and placed our trust in Him (4:5;5:8). Being the undeserving recipients of God's mercy towards us, we have lost our rights of being able to judge anyone else. If we have received this forgiveness of our sins freely from God, we have no right to be unforgiving towards anyone else. That is the lesson of the parable of the king and the two servants in Mt.18.
If we have been properly humbled by having to go to God in humility and honesty and acknowledge and confess our sins to Him without trying to justify any, we would not even have the heart to want to take revenge on others or to want to see them suffer for their sins. Now ask ourselves what we do with the account of wrongs we have suffered from others!
The right way to deal with the sins of others against us is to forgive them. When God tells us to do this, He tries to help us by reminding us of how we ourselves have been forgiven (Ep.4:32;Co.3:13). Then we can make a decision in our mind and forgive them as a matter of choice.
When the entries from the account in our mind concerning others come up for attention, we can then remind ourselves that the debt has been cancelled. When we do this regularly in our mind, we can overcome even the whispers the Accuser makes against others, and we will also find that our feelings don't trouble us as strongly as before.
By forgiving others we are not pretending as if they haven't done any wrong or that they haven't affected our lives. We may be still suffering from the consequences of those wrongs. But what we are affirming is that we have let them go free from our hands, and placed them in God's hands who will deal with them wisely, righteously, justly and mercifully (Ro.12:17-19).
When we were going over the accounts again and again and waited for judgment to fall on the others, it was we who suffered from sleepless nights and heartburn! How foolish and silly!