Need help understanding this about the jhanas I am reading
 "A Critical Analysis Of The Jhanas"

And it's talking about the way to reach the first jhana. This passage below.


  Block quote
  The Pa:isambhidāmagga explains them as follows: 
  For one developing the first jhāna, the hindrances are abandoned by way of 
  suppression. For one developing concentration partaking of penetration, 
  wrong views are abandoned by way of substitution of opposites. For one 
  developing the supramundane path that leads to their destruction, 
  (defilements) are abandoned by way of cutting off. At the moment of fruition 
  they are abandoned by way of tranquillization. And abandoning by deliverance 
  is nibbāna, cessation.2
   (Wr. tr.).
  `


The question is, isn't the first jhanas all about concentration? So why did it say if you want to reach the first jhana you must partake in abandonment by suppression, and to reach concentration you must abandoned by way of substitution of opposites. Isn't it all dedicated to concentration?
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.