When I think about holiness, I tend to compare it to impurity. One time somebody explained to me that when God created us he made us to be good, like a clean cup of water. When we sin, even if it's just a tiny sin, it is like putting a drop of red food coloring in the cup of water. No matter how small that drop of red food coloring is, all of the water in the cup will turn red. No matter how little we sin, we are completely sinful, because we all have sinned. Romans 3:23 says "For all have sinned and fall short of the glory of God." God cannot be around anything that is even a little bit unclean or sinful. We are completely sinful, so how can we talk to and pray to God? How can we say that God is in us as Christians?
When Adam and Eve sinned, God wanted to spend time with them and all other people so much that he made a plan to clean anybody who wants to spend time with him too. Since sin is so bad, this was not going to be an easy job. It would take someone who was completely clean to die for everyone who was sinful. Everybody on earth had sinned, so a normal person could not do the job. Instead, God sent his only son into the world to become a human, so that we could be clean. He went through so much pain so that we could be sanctified (cleaned) and so that we could be with him again. It is so amazing to me that we can be with God and talk with him, because he has cleaned us even though we don't deserve it!
