From person to person, generation to generation, from one corner of the world to another. Words are tools that enable the otherwise not very formidable human race to dominate other species. There are good tools and poor tools. As with any other tools, proficiency requires practice, good training, good tools, good material, a clear idea of the goal, patience, and persistence. Words can bring the word-worker fame and fortune, or at the least, the satisfaction of constructing something useful, or repairing something, or maybe even creating something new and beautiful.
Words can clarify.
Words can obscure. Words can do great good. Words can do great harm. Words can be addictive. People can get so addicted to reading, writing, listening and talking that they neglect even routine activity.