"Come now, let us reason together, says the Lord..." Isaiah 1:18
When Jesus commands us in Matthew 18 to go to our brother if he has sinned against us and tell him his fault that he might listen and you may gain a brother, that isn't some new way of dealing with people...its been God's way since the beginning.
God is the first example to us this. He has just listed off all the people's wrong yet he does not pour judgement first. No, first he says let's get together and talk reasonably about it and not continue in ignorance of where we stand with each other. He then promises forgiveness and blessing if the repent and turn back to Him. He comes to us and says, "Hey, here is what you have done, lets see it as it is and move forward in grace and forgiveness." Which is exactly what we are to do with each other. To come together and see ourselves and our actions for what they are (not what we want them to be or how we want to see them) in relation to each other so that we can acknowledge, repent, forgive, and move forward together in love and grace.
When God asks us to do the same in Matthew, remember that he exampled it first. He is not asking us to do something cause he decided its what is best for us (which in theory would be a good enough reason), but actually he lets us in to his world, into his secret family recipes, and says "Hey, let me tell you my secret to reconciliation...it works every time."