"Christianity has an image problem." - David Kinnaman, The UnChristian
Human beings are made in the image of God. God directs His people to live holy because He is holy. God offers His Word, so that His people can follow His Word in their daily lives. God sent His only begotten Son to earth to redeem mankind into a relationship with Him and for Christians to follow the example of Christ.
However, the biggest issue that most people who do not accept the faith of Christianity due to Christians. Actually, the issue has more to do with the hypocrisy of Christians than it does with Christians as people in general.
The Christian is to live as an example as much as he or she is to live by example. When we follow that example, others tend to gravitate towards us and follow us in our walk with Christ. When we fail to follow that example and others witness us, we send mixed messages and cause others to become confused. If we want to win souls for the Lord, we need to provide a witness that gives a positive example to others.
Follow my example, as I follow the example of Christ. - 1 Corinthians 11:1 (NIV)