Words are what your mind is built of. You are a collections of thoughts and beliefs, expressed and communicated by words. You are affected by other's words and beliefs.
Words can change you more than physical pain. For those of us with 'normal' lives, words play a much larger part in building our beliefs than does physical pain. The potential of words is what gives us everything that lower animals are not. This includes much power to hurt.
Perhaps the greatest way that words can hurt you is by cutting you off from people whose words you don't like. If you ignore them, you loose touch with an enormous percentage of the population. Or if you hate them, instead, you live with a negative emotion. Or maybe they change you, or the way that you think, often in negative ways.
No one who cannot keep their thoughts from being changed will have a good life. Many people work hard to make sure that this is so. Jerks.
It's only words
And words are all I have
To take your heart away.