Well most people in this world dont realize that Christianity is not a RELIGION. Its a lifestyle (to live Christ like). Most people dont understand that. I think most people that dont believe is cause of the Unknown.
But make some points for people that dont believe...you may say "How can I believe in something I can not see?" Well do you believe in the wind or the air you breathe? You may not see it but you see the effects they have in life. Sometimes the simple things in life can explain or lead us to understand there is a GOD.
Well many people today claim they are agnostic. Which means: without knowledge or unknown. There's the term UNKNOWN again. Well evolution is what most of them believe. Read this bit of info. how evolution is false: http://www.biblelife.org/evolution.htm
I think most people dont want to believe in a GOD is cause they have to answer for how they lived their life. Its easier to just live you life, do want you want, and not care about anyone else but yourself. That's why people want to turn away from the unknown. Its easier to just live like you want and not answer for the negative things you do. Plus its hard to live like a Christian. Yeah Christians are no near perfect. We all fall short of God's grace but by faith in HIM we are saved.
But in my life I do not look up to any man or hold some religious leader up. I do not follow anyone but the life that Jesus lead and explained how for us to live. Only God can judge you...
that's my 2 cents...