While reading though the forums on aikiweb, I came across this link. There, the author writes about why we train with weapons in Aikido (although, in my opinion, the answer applies to many martial arts).
I highly recommend checking it out. I think it’s a well-written response to a common and excellent question. What I like most about the answer (sorry, I’m about to spoil it a bit for you) is the re-phrasing of the question: “Why do we practice with weapons?” to “What do learn from practicing with weapons that we do not learn anywhere else?”
What I enjoy about this re-phrasing is that, quite often, I find myself thinking: “Why?” Why do we move one way, and not another? Why do wear hakama, instead of sweats? Why do we bow? But the question “Why?”, as the essay I am linking to illustrates, may not be enough. The truth is, almost any action, if done with deep conviction and intention, can provide a level of self-understanding. When I expand the question to “What does this particular action teach us, that another action cannot?” I have to think harder about the answer.