Just because you pick up a sword and train doesn't mean your are committing an agressive act. I am a peaceful person, yet I train my body to be a formidable weapon, this is just how I set myself at ease. Training to fight and being violent are two different things. Simply having the capacity to kill someone isn't, to my knowledge, a contradiction of your faith (I'm assuming its Christianity or of that ilk.) Hope I've been of assistance.