Need help understanding this about the jhanas
I think this passage is addressing something that's more explicitly stated elsewhere.  In the Jhana Sutta (AN 9.36), for example, we find:  


  secluded from sensuality, secluded from unskillful qualities, [he] enters &amp;
  remains in the first jhana: rapture &amp; pleasure born of seclusion,
  accompanied by directed thought &amp; evaluation.


The operative word here, of course, is "secluded".  Vitaka and vicara (i.e. concentration) only come into the equation once rapture and pleasure are born of that seclusion.  Piti and sukkha help to calm, gladden, and focus the mind allowing concentration to strengthen in to full jhana.  

So of course, this begs the question of how one finds that seclusion.  There are some who are lucky and can just shut the door on their negative and unwholesome states.  Other have to win their seclusion through other methods like suppression and substitution of opposites.  I think the latter group is who your quoted passage is addressing.