Quote 43
For we can neither employ them in handicraft or agriculture; we neither build houses (I mean in the country) nor cultivate land. (7)
Lazy absentee landlords typically built huge estates, further contributing to Ireland's poverty.
Quote 44
For we are told by a grave author, an eminent French physician, that, fish being a prolific diet, there are more children born in Roman Catholic countries about nine months after Lent than at any other season. (13)
Here's another satirical reference to Ireland's Catholicism and the Lenten practice of eating fish. Fish was supposed to boost fertility.
Quote 45
As to our city of Dublin, shambles may be appointed for this purpose in the most convenient parts of it. (16)
Shambles are slaughterhouses. Swift is painting a picture of a lovely Ireland, isn't he?