Commentary Par XXIII 11-12

Unriddled, these lines indicate the heavenly equivalent of noon on earth, the zenith of the universe.  We remember that the physical sun lies below the place where Dante finds himself.  Beatrice is expecting 'sunrise' there, at the zenith, not at the 'horizon.'  The descent of the blessed spirits of the Empyrean, naturally, is from 'true north,' the very top of the universe.  Lombardi points out (DDP Lombardi.Par.XXIII.11-12) that the heavenly Jerusalem is directly over the earthly one; this 'supernatural sunrise' calls our attention to the fact that the 'sun' that is about to 'dawn' is indeed extraordinary.