Why couldn't God just forget sins?
"If God is a really a loving God, why doesn't he just forgive everybody? Why did Jesus have to go through suffering into death? Why did he have to be a ransom?
"Here's the beginning of the answer: Jesus didn't have to die despite God's love; he had to die because of God's love. And it had to be this way because all life-changing love is substitutionary sacrifice.
"...God who is more loving than you and I, a God who comes into the world to deal with the ultimate evil, the ultimate sin, would have to make a substitutionary sacrifice. Even we flawed human beings know that you can't just overlook evil. It can't be dealt with, removed, or healed just by saying, "Forget it." It must be paid for, and dealing with it is costly."
-Tim Keller