"God is whoever raised Jesus from the dead, having before raised Israel from Egypt." This is the hallmark sentence of Robert Jenson's Systematic Theology. It is an elegantly simple but dauntingly deep sentence, which took Jenson a lifetime of theological reflection to write.
To write such a sentence requires that we discipline our presumption that we know what we are saying when we say the word "God." For it turns out that we are most likely to take God's name in vain when we assume we know what we are saying when we say "God."
Indeed, one of the ironies of the recent spate of books defending atheism is the confidence these "new atheists" seem to have in knowing which God it is they are sure does not exist. They have forgotten that one of the crimes of which Romans accused Christians - a crime whose punishment was often death - was that Christians were atheists.