Former posting:  Perhaps Keats was closer to VN's heart than to his conscious mind - for I'm thinking now about an uncommon word, mainly employed in heraldry, which appears in Keats' poem when he describes emblazoned stained glass reflections ( "warm gules"*) ... when he blends heraldic motifs and colored vitraux...In "Spring in Fialta":
 "At the beginning of his career, it had been possible perhaps to distinguish some human landscape[   ] through the stained glass of his prodigious prose... but with every new book the tints grew still more dense, the gules and purpure still more ominous; and today one can no longer see anything at all through that blazoned, ghastly rich glass and it seems that were one to break it, nothing but a perfectly black void would face one's shivering soul."

Jansy Mello (resuming a monologue): Stainglass windows and harlequin motley shades enchanted Nabokov from his childhood onwards, as did all kinds of mirrors, prisms, rainbows, blown-glass and spirals in transparent marbles. In "Spring in Fialta" the tints of his prose grew "still more ominous" impeding the passage of light through blazoned glass.

If, when he wrote that "it seems that were one to break it, nothing but a perfectly black void would face one's shivering soul," V.Nabokov was making a reference to the Biblical lines in 1 Corinthians 13:12 (KJV) ["For now we see through a glass, darkly; but then face to face: now I know in part; but then shall I know even as also I am known"], the reader will then need to puzzle out what kind of "soul" or "face" would confront him (V. or the reader) on the other side of the glass partition.

I don't think that VN had, at all, "God's Face" in mind (should we accept the biblical reference): he was probably indicating the reader/Author relationship. In the present short-story Ferdinand's dismissal of "human landscapes" and his pointless verbal embelishments would be erecting an unsurmountable barrier between the writer (as also the reader) and his shrivelling soul.  

However, VN might have suggested the Author's profound relation to his own finished work instead. That seems to have been Prof. Hurley's vision (quoted by CK in "Pale Fire") : "None can say how long John Shade planned his poem to be, but it is not improbable that what he left represents only a small fraction of the composition he saw in a glass, darkly."* Here we may admit that there is an eerie antevision of the fate, the "black void" that awaits the reader of his posthumously published "The original of Laura."  

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*note the change from the KJV to another interpretation, closer to Martin Luther's reference to the glass-mirror, by the move from 'through a glass' to 'in a glass'; note the change from younger Nabokov's religious or philosophical stance to the one he adopted in the future...