I have gone to church most of my life. So in some sense, I have been a Christian for a long time. But when did I decide to make God the focus of my life?
After my freshman year in college, I really started to think about questions like “why am I here?”, “what is my purpose in life?”, “does God exist?”. I would say at this time I was definitely an agnostic. The only thing I needed to believe that God existed was scientific evidence. I read many books at this time, some of which include The Tao of Physics, A Brief History of Time, Zen and the Art of Motorcycle Maintenance, World Religions, The Fingerprint of God, Perfect Health. I went and listened to debates between scientists and Christians on the existence of God (Dr. Hugh Ross). At this time I was very naive and impressionable, and was heavily influenced by new age type religions, as well as Metaphysics and Taoism. It just seemed too easy to say that God created everything.
I really did not start to believe again until I talked with Dr. Hugh Ross and went to his debate against all the physicists and scientists. Hugh Ross basically uses the Anthropic principle to justify a means for a God. (The physicists biggest argument was that just because all of this scientific exactness exists, it doesn't mean that God created it, it just means that it was created. I have always tried to look at both sides of the picture. I think alot of people will read what they want to believe and not read other peoples views. In other words, they will read people stories on the Existence of God, but not read peoples essays on why they don't believe in God.)
I was very interested in this, but I have always believed that one cannot objectively prove Christianity with science without some reason. So I studied philosophy and tried to put together a philosophical basis for using science as a basis for proving Christianity. The result of my pursuits was the following essay: Philosophical Reasoning for the Existence of God: The Anthropic Principle.
As soon as I realized that the existence of God cannot be proved (after reading a few more books: Quest for God, Religion within the Limits of Reason Alone...), I quit trying to prove objectively, philosophically, etc. that there must be proof. It wasn't until I decided to walk the Christian life again until I realized how we can know Christianity is true. I cannot explain this basis for truth in words because it is a feeling that transcends our normal bodily functions, and can only be acquired by first believing in Him.
But I will try to explain. God's presence is revealed to the Christian in very subtle ways. For example, when I am “close” to God (i.e. praying and reading the Bible frequently, in other words being obedient) I am compelled to do things that I would have never wanted to do. I am compelled to be selfless, to think of others. I am compelled to be honest, to follow all laws and rules. It's as if my conscience is in supersensitive mode.
Why am I compelled to do good? What makes me want to be selfless when I am so selfish by nature? What motivates me to do good when all I am doing is praying and reading the Bible? I am not praying that I will do good; I am not trying to believe that I am a good person. I am just compelled to do good works and I cannot explain it. But if I fall away from God, I become selfish, don't care too much about rules or anything, and I am constantly seeking happiness by buying little things or going out drinking, etc.
In closing, until you first take a step to believe you will never be able to know that God does or does not exist, because the proof lies in divine truths which cannot be understood with only reason and sensual perception.