I never supposed Bishop Berkeley
Would seem, as a spectre, so sparkly.
It’s frankly nightmarish
To see him so garish
Especially through a glass, darkly.

Berkeley argued that what we see exists only in the mind. If this is indeed a spectre, it would seem to be offering some kind of ironic comment on that theory. More probably, however, our narrator has been the victim of brainwashing by pious parents or Bible-bashing teachers in high-school.