Belief in God is rational.
Everything has a cause. So unless there is a first cause, then you would have an infinite regress. And then nothing could exist. Therefore there must be a first cause. Therefore God, the first cause, exists. QED.
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29.6.16
r90 slightly edited. This probably needs a lot of editing but if I do not put it here I can easily just forget about it. And unless God grants to me some kind of inspiration I have no idea how to edit it.