The reason why God matters is because it provides a real reason as to why we are here beyond what we arbitrarily construct for ourselves.

It's a good question because all we get is how did creation come to be but it offers us no explanation as to why creation exists and what our purpose is in it.

I'd also argue that the reason why culture has become so fixated on identity issues and finding our "authentic self". I actually don't think they are terrible questions.

The problem with the approach is that we presume the answer is within rather than without. In Christianity we are endowed with purpose and meaning by God. In secular thought we endow ourselves with subjective purpose and meaning.