I believe in God because I have felt the presence of God. I have been moved by God while looking in to the eyes of the Elder at Chalice saying, "The body of Christ, the cup of Salvation." I have been moved by God when filling a water tank in the Sonoran desert. I have been moved by God when I spied an old friend at my father's funeral.
I recognize the presence of God with the same power of perception that shows me Love and Beauty. My physical senses provided the data, but Love and Beauty are present at another level of abstraction. The physical world is like a carrier wave; Love, Beauty, and God are like messages carried on it.
A radio signal can be fully described, in some sense, by a Time-Frequency or Time-Amplitude plot. But if there is a message encoded on the signal, then there is more to be known about the signal than the particular modulations of the frequency or amplitude.
Likewise, the human experience is more than a series of electro-chemical reactions. Life is different from non-life. To reduce all human existence down to the physical world leaves no room for the Soul which observes super-natural things like Love, Beauty and God. Now, there is no physical, or natural, evidence of supernatural things. But my explanation of a world that is more than the natural world better fits my experience than a world that is only physical.
Sam Harris recognizes the need to feed the soul, although he thinks irrational religions are not the way to do it. I've witnessed much suffering and loneliness among those who neglect their non-physical selves. But what about my friends who profess to only believe in the physical world, but are happy? It is a bit of a conundrum for me; as my faith is a conundrum for them.