I'm simplifying things considerably, but Gervais essentially argues that "science can't prove God exists." I've always found this line of reasoning to be faulty because "science" seems to be the wrong tool for the job.
No one argues that "hammers are useless because yesterday I tried to screw in a lightbulb and my hammer just kept breaking them to pieces." Likewise, no one says "I don't believe in poetry because..." and then finishes that sentence with the same objections they bring to the God vs. Science Debate.
Poetry doesn't exist chiefly to tell us how molecules interact, but a good poet could probably tell that story in a compelling way. Poetry exists, and has its power, because it gets to a part of us in a way that nothing else can.
Science (do I really need to write this sentence?) is abundantly valuable and useful. But it cannot (nor should it) do for us what religion or poetry can.
This isn't the final word on "why I believe," but, among other things, faith in Christ helps me make sense of myself and this world in ways that science and even poetry never could.