But a little reflection will show that speech and its offshoot, the written word, can have enormous consequences for good or for harm. In fact, whereas for beings such as animals who live at the preverbal level physical action is of dominant concern, for humans immersed in verbal communication speech gains the ascendency.

Speech can break lives, create enemies, and start wars, or it can give wisdom, heal divisions, and create peace. This has always been so, yet in the modern age the positive and negative potentials of speech have been vastly multiplied by the tremendous increase in the means, speed, and range of communications.

The capacity for verbal expression, oral and written, has often been regarded as the distinguishing mark of the human species. From this we can appreciate the need to make this capacity the means to human excellence rather than, as too often has been the case, the sign of human degradation.

Source: http://www.vipassana.com/resources/8fp4.php

For more on the Buddha's teachings on Right Speech, please visit:

Family Dharma: Right Speech Reconsidered
http://www.tricycle.com/web-exclusive/family-dharma-right-speech-reconsidered

Characteristic Of Right Speech
http://www.buddhapadipa.org/dhamma-corner/characteristic-of-right-speech/