[Spoiler Alert]
We later learn that Blazes Boylan is a man with whom Molly is having an affair, hence the attempt to hide the letter out of sight and brush it off as a work-related matter - even though Bloom already knows about the extra-marital relations. He himself is also engaged in a (solely) epistolary affair with a woman named Martha Clifford, whose letter to Bloom we see in the next chapter. This marks an instance that slips by, but it actually contains a lot of information on the upcoming narrative and insight into the Blooms' marriage.
