Not P but Moby-Dick (25)

[Mike Jing]

>From Chapter 42:

Why to the man of untutored ideality, who happens to be but loosely
acquainted with the peculiar character of the day, does the bare mention of
Whitsuntide marshal in the fancy such long, dreary, speechless processions
of slow-pacing pilgrims, down-cast and hooded with new-fallen snow?

What does "the peculiar character of the day" refer to here?