Sentence:  Here we can explain only in these broad outlines why the asking of the question of being is in itself through and through historical, and why, accordingly, our question as to whether being will remain a mere <WSD>vapor</WSD> for us or become the destiny  of the West is anything but an exaggeration and a rhetorical figure. 
Meaning of the word marked with <WSD> tags:  Something insubstantial.