Why did Bloom experience a sentiment of remorse?

Because in immature impatience he had treated with disrespect certain beliefs and practices.

As?

The prohibition of the use of fleshmeat and milk at one meal: the hebdomadary symposium of incoordinately abstract, perfervidly concrete mercantile coexreligionist excompatriots: the circumcision of male infants: the supernatural character of Judaic scripture: the ineffability of the tetragrammaton: the sanctity of the sabbath.

How did these beliefs and practices now appear to him?

Not more rational than they had then appeared, not less rational than other beliefs and practices now appeared.

What first reminiscence had he of Rudolph Bloom