Sigmar is viewed as a a shard of the Heavens by Balthas.
"The God-King stood before him, arrayed in golden war-plate. The air twisted about him, as if the realm were not quite able to bear his weight. He stood half a head higher than the tallest of his warriors, and there was an elemental strength to him – as if he were the raw fury of the storm, given solid form. But his presence was not merely physical. Sigmar’s immensity stretched beyond the boundaries of the corporeal, into spheres beyond the sight of mortal men. He was the cold gaze of the moon and the warm laugh of the sun. He was the sound of clashing steel, of avalanches and howling winds. To one possessing storm-sight, Sigmar appeared as a shard of the firmament itself. A being of pure starlight, impossible to look at for long. The God-King was Azyr, given mind and voice. In his merest gesture was the movement of worlds, and in his gaze, the flare of falling stars. Balthas blinked, trying to ignore what lay behind the mask of broad, too-human features. The face of a man aeons dead, out of whom a god had emerged"