Level of courage is like your personal level, at first it was easy to level up but over time it becomes more difficult to improve progressingly. Increasing level of bravery will give you access to the teeth that the other players below the level of courage no access too. Once you reach the highest level of confidence you will have full access to every part of the PvP gear out there. Personally I find this to be the system most useful and fun because you can level your own pace and not feel the need to cram stuff for a week like what you are forced to do in WoW.
If you have further questions about the system of bravery or want more details, please feel free to check my points to get the guts start guide.