In short, Isaiah is about Jesus Christ, the God-man, who dwells in the midst of his people and transforms them into his bride. And the two will become one. Isaiah is about the marriage feast of the Lamb of God.
It is quite a feat after twenty-some-odd years to come back as a band and create something that fits nicely into the corpus of their prior work and, at the same time, propels their sound forward into unsettled territory.
It is not the words that are really empty. It is men themselves when they speak and hear empty words. It is the I which is emptied in relation to the Thou, one empty subject confronting another.” Karl Barth