Talk:Aura/@comment-28257386-20140717050620/@comment-10380701-20140717161520

Think of Aura as a combination of a body armor (lowers damage) and an MP gauge. When you get hit, your Aura goes down.

The aura barrier that Ren used doesn't just protect him, but it also stopped the Taijitu's attack. It's most likely far stronger than a regular aura, but only covers a small portion.

It's essentially focusing most of your ki into one portion of your body for offensive and defensive purposes. Both of which Ren demonstrated.

That said, to answer your question, it's for the same reason that knights have shields. An armor is useful on it's own, but it won't stop everything.