Fasting from words, fasting from a volume of speech, being willing to humbly accept the yoke of silence and quietude deprives the tongue of the mastery of our hearts and minds. The tongue is a very useful tool for the art of love and for the art of prayer, but it is also the means by which we afflict others and even our own selves so often. So it must be called into holy obedience.
People have always wondered at the saints, that they are able to walk around serene, whatever happens. But that is because they can choose where they'll be. They don't have to be angry. You see the difference between having scattered emotions and having a fully vibrating, controlled emotional body. This body is made from energy created from choice, from the effort involved in making choices. But it is necessary to practice; then something is possible.