I'm a Christian, but I have to disagree with your reasoning. You say that everything must have a cause. This is true. But this is a law of the universe. That's why God, being outside the universe, doesn't need a cause. So far, that's right. But, while events IN the universe require a cause, the START of it doesn't. Think about it. The start of the universe is also the start of all laws. Therefore, the law of causality does not exist, and therefore does not apply, during the creation of the universe