If a Christian is not able to see that a change has taken place in their life, then they would think that Christianity to be based on a falsehood that they could not accept.
We have all seen Christians that are hypocrites, but for every hypocrite we can think of two or three who grow more and more like Jesus-kind, loving, considerate, and free from guile.
However, sin in the life of a Christian remains, even in the lives of those we consider to be the best Christians.
  We see people from the outside, and we can seen that their relationship with Jesus has brought dramatic changes to their lives; that as time goes on their lives become more and more like Jesus.
But when you ask these people about their relationship to their Lord, they likely would reply that they realize more and more how sinful they really are, and how much more they need to depend on Jesus.
  So we learn that their growth as Christians is in their increasing dependence on Jesus.
I don't know what your experience as a Christian has been like, but for me, I find that I must continually relearn that when I am apart from Jesus I cannot help sinning.
The more I understand myself, the more I realize how very much more I need Jesus.
  So what is it really like to be a Christian? It is to realize that without Jesus we are lost.
  That our life is really worth nothing without Him.
That there is nothing in this world that will bring true peace and happiness if Christ is not the center of our lives.
  As we grow as Christians, we grow more dependent on Christ.
As we experience in our own lives the new life that Jesus has brought, we will experience the blessings of peace, acceptance, and joy.