Being born again (in the Holy Spirit) only takes a moment. But becoming like Christ takes a lifetime. It is that simple.
But there is great tension in the Christian experience. We agree with God's commands --- but we cannot follow them. As a result, we are painfully aware of our own sin (way more than non-Christians). We know that we are hypocrites --- and we don't like it any better than those who are watching us do.
It is the process of sanctification. It is the character and nature of sanctification.