The power of typography is in the way language can be transformed simply by the way you use type. The art of typography is to accurately embody the intended message in what you write, and to do so well. If text is intended to be read, the typography must be readable. If text is meant to convey power or authority, it must have a strong presence on the page.
Typography gives language a body with which to move and breathe; it a way to convey specific meaning. In much the same way as actors bring different interpretation and flavour to particular characters in a play, so too do choices in typeface selection and type-setting choices bring unique meaning and tone-of-voice.
Typography matters because what we communicate matters. It is our responsibility to care deeply about the way we communicate them.