"God" has a connotation in the sentence "There is a God." It is an evocative sentence which does much more than attempt to refer to a thing of a certain description. It entails that the fact that there is this world, rather than nothing, is very good, and that the situation in which we find ourselves makes living in this world well worthwhile and the lives we have in it things to be deeply grateful for. When the priest kisses the cross or the Jew reads the creation story, this connotation is never far away from these signs.
As an attempt at a reduction of religious language to naturalistic language, this gloss on "There is a God" fails, however. This connotation of "There is a God" is, when the theist utters it, not "what he means." He means to refer to a supernatural person who created this universe. So there is no reduction of "God" to the goodness of the fact of this existence or the appropriateness of being glad for it.
Yet there is more to this story, as we'll see in the next post.