The purpose of typography

Regardless of era, culture, language, or medium, typography has evolved as both a science and art for one main purpose: to make Words easier to understand and more meaningful to read.

From the creation of individual letterforms, to Words, to lines, to paragraphs, to pages, to books, typography is manipulation, control, and experimentation of how to use type to express meaning in the ideas the letters attempt to communicate.

Source : http://www.toddroeth.com/class/grph_210/23/01-introduction