Imagine that your best friend has just been sprayed by a skunk, and now he calls you up. He hasn't been cleansed. He calls you up and he says, "Hey, David, I'd like to come over and spend some time with you." Well, now you may feel fine towards your friend. I mean, you still love him and you like normally being around him. However, until something changes, you are not going to be able to invite him into your home. You're not going to be able to have close fellowship.
There's going to be an alienation between the two of you, not because you have to change, but because he has to change. So it works that way with the atonement. We needed changing. We needed cleaning up. God didn't need to change at all. But a holy God cannot have close fellowship with a person who is unholy.