I, like KathyK am having a little trouble with this question. However, I believe that the concept of adoption encourages us because God chose us. We haven't done anything to deserve Christ's adoption of us - but He chose us so that we could be adopted into His family. Much like a "traditional" adoption, He loves us and chooses to take care of us unconditionally. He adopted us simply because of His love for us.
This is encouraging because sometimes children are adopted because no one cares or wants them. In our case, God wants us and He wants to have a relationship with us. He cares for us and there is nothing that we can do about it.