I believe that scientists like Sagan, Feynman, Hawking and others who have adopted a positivist outlook on the world make a mistake when they reduce Christianity to a mere philosophy and analyze it purely in that way – which is to say, from the outside (as an idea, merely) – from the position of having never experienced the grace of God and the indwelling of the Holy Spirit. And I agree with them, given these criteria. Christianity is not an argument that can be explained from the outside in the absence of God’s graces any more than love can be explained to a robot.
Arguments and experiences are certainly not the same thing and more importantly, the latter can never replace the former. For example, when you are in love, you seek to understand that love and you use reason (and even arguments, perhaps) in your search to understand your experience – but if you are not in love, no amount of reason will produce the love you do not have. If you close your heart and turn your back on God’s invitation to know him then there is nothing anyone can say – there is no argument – that will fill in the gap left by that refusal. If you have not experienced Christ then his story will not correspond, will not resonate in you. In the absence of the Holy Spirit, mere philosophy will not do. For Christians, it is a recognition, a correspondence of lived experience through the Holy Spirit that draw us to Christ, who we come to know as he reveals reality to us. It is reality, not mere philosophy that draws us. Christianity is a relationship with a person, not an idea.
I say this because it should not frighten or concern us that someone who has not met this person should try to dissuade us from our relationship with an idea, as if someone could argue a mother out of her love for her child.