Explanation in the manual:
Repel Damage (Passive) - Some of the force behind your opponent's attack is sent back to him.
Reflect Missiles (Passive) - Any missiles fired at you are reflected back to your opponent.
In other words, if you take both, no enemy can hurt you without hurting him/herself. I never tried it, but if you think about it, it actually sounds like a good way to invest skillpoints. Maybe next time.
