Your boundless rage grants your blows extra strength, though at the expense of accuracy.
Benefit: When you use Power Attack while raging or while using raging song, you take an additional –1 penalty on melee attack rolls and combat maneuver checks, and you gain an additional +2 bonus on melee damage rolls. Modify this damage bonus appropriately based on the type of weapon you are using, as normal for Power Attack.
Pathfinder Roleplaying Game: Advanced Class Guide © 2014, Paizo Inc.; Authors: Dennis Baker, Ross Byers, Jesse Benner, Savannah Broadway, Jason Bulmahn, Jim Groves, Tim Hitchcock, Tracy Hurley, Jonathan H. Keith, Will McCardell, Dale C. McCoy, Jr., Tom Phillips, Stephen Radney-MacFarland, Thomas M. Reid, Sean K Reynolds, Tork Shaw, Owen K.C. Stephens, and Russ Taylor.