I've read a lot of Harold Bloom through my English education. Great guy. The authority. I mean, THE authority on all things literature.
That's why this makes an even greater impact to me. He is talking of his favorite book of The Bible and the very second sentence of his little essay:
"A sly masterpiece of four brief chapters, Jonah reverberates in Herman Melville’s Moby-Dick, where it is the text for Father Mapple’s grand sermon."
This sentence is setting up the fact that this is how important Jonah is--it is used in one of the great novels, almost as a base. Basically, Moby Dick would not exist without Jonah.
He then needs to reference it again, as if putting it into perspective, using Moby Dick as the reference point of the perspective, as we all supposedly know Moby Dick:
"There is of course the giant fish (not, alas, a whale) who swallows up Jonah for three days but then disgorges him at God’s command. No Moby Dick, he inspires neither fear nor awe."
Again, anybody that seems to have to mention WHALE has to mention Moby Dick!